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ANATOMY 

OF   THE 

BRAIN  AND  SPINAL  CORD 

SANTEE 


ANATOMY 

OF    THE 

BRAIN  AND  SPINAL  CORD 

WITH  SPECIAL  REFERENCE  TO 

MECHANISM  AND  FUNCTION 

FOR  STUDENTS  AND  PRACTITIONERS 


BY 

HARRIS  E.  SANTEE,  M.  D.,  Ph.D. 

PROFESSOR   OP  ANATOMY  IN  THE   COLLEGE   OF   PHYSICIANS   AND  SURGEONS,  MEDICAL  DEPART- 
MENT,   UNIVERSITY    OP    ILLINOIS;     PROFESSOR    OF     ANATOMY    IN    JENNER    MEDICAL 
COLLEGE,   CHICAGO;  MEMBER  OF  ASSOCIATION   OP   AMERICAN  ANATOMISTS. 


FOURTH  EDITION,  REVISED  AND  ENLARGED 


WITH  128  ILLUSTRATIONS,  33,  OF  WHICH  ARE  PRINTED  IN  COLORS 


PHILADELPHIA 

P.  BLAKISTON'S  SON  &  CO. 

1012   WALNUT   STREET 
1907 


Copyright,  1907,  by  P.  Blakiston's  Son  &  Co. 


Printed  by 

The  Maple  Press, 

York,  Pa. 


PREFACE 

The  author  hopes  that  the  present  edition  of  this  work  may 
receive  from  his  colleagues  the  same  generous  consideration 
accorded  to  the  former  editions.  His  endeavor  has  been  to  set 
forth  the  present  status  of  the  anatomy  of  the  human  brain. and 
spinal  cord.  To  do  this  the  facts  have  been  gleaned  from  many 
sources;  and,  so  far  as  was  possible,  from  the  original  sources. 
Being  designed  for  a  text-book,  the  subject-matter  is  presented 
in  the  order  found  convenient  to  the  dissector.  The  description 
proceeds  from  the  gross  structures  to  the  constituent  neurones  in 
each  successive  region.  Wherever  the  embryology  will  assist  the 
student  to  comprehend  the  adult  forms,  the  development  is  briefly 
given  in  the  text ;  but  a  special  chapter  is  also  devoted  to  embry- 
ology, which  presents  a  concise  and  connected  statement  of  the 
development  of  the  entire  brain  and  spinal  cord. 

The  special  objects  held  in  view  throughout  the  book  are  the 
location  of  functional  centers  and  the  tracing  of  their  afferent, 
associative  and  efferent  connections.  Particular  emphasis  is  laid 
upon  the  origin,  course,  termination  and  function  of  conduction 
paths  as  they  are  met  in  the  regular  study,  and  the  more  im- 
portant and  better  known  of  these  paths  are  summed  up  in  a 
final  chapter  on  the  tracing  of  impulses.  Function  is  ever}^where 
correlated  with  structure;  and  so  far  as  present  knowledge  per- 
mits, the  function  of  each  group  of  neurones  is  given  in  connec- 
tion with  its  anatomical  description. 

The  BNA  Nomenclature  is  followed  almost  without  excep- 
tion, the  English  equivalents  of  the  Latin  terms  being  very  largely 
employed. 

Keeping  pace  with  the  lectures,  every  student  is  expected  to 
dissect  the  human  brain  in  the  laboratory,  exposing,  studying  and 
sketching  every  macroscopic  structure  as  it  occurs  in  the  work; 

v 


433320 


VI  PREFACE.- 

and,  then  with  the  microscope,  examine  the  minute  structure  and 
picture  the  histology  of  the  same  parts.  For  these  purposes  the 
class  should  be  taken  in  small  sections,  divided  into  groups  of  two 
to  four  students,  and  each  group  should  be  provided  with  a  well 
hardened  human  brain.  It  is  desirable  that  each  student  should 
receive  a  well  stained  microscopic  section  of  every  important  part. 
This  is,  however,  often  impossible;  and  the  instructor  may  get 
along  with  considerable  satisfaction,  by  having  the  students  ex- 
change, if  he  has  but  a  few  sets  of  slides. 

The  author  wishes  to  acknowledge  his  indebtedness  to  recent 
literature  and  to  standard  works  on  anatomy.  McMurrich's 
"Development  of  The  Human  Body,"  Barker's  "BNA"  and 
Barker's  "  Nervous  System,"  the  work  of  Dr.  Alfred  W.  Camp- 
bell, "  Histological  Studies  on  the  Localization  of  Cerebral  Func- 
tion," the  "Text-book  of  Anatomy"  and  "Memoirs  "  of  D.  J. 
Cunningham,  F.  R.  S.,  and  the  fourth  edition  of  Morris's  "  Human 
Anatomy"  have  been  especially  useful. 

I  desire  to  express  my  appreciation  of  the  kindly  assistance  of 
my  colleague,  Prof.  Wm.  T.  Eckley,  M.  D.;  and  to  say  that  the 
artistic  merit  of  the  new  illustrations  in  this  book  belongs  to  my 
friend  and  pupil,  Mr.  Zan  D.  Klopper,  of  Chicago,  who  sketched 
the  original  dramngs  from  my  own  specimens.  My  thanks  are 
also  due  to  the  publishers  of  this  little  monograph,  for  many 
favors  and  courtesies  shown  me,  particularly  for  allowing  me  to 
select  illustrations  from  Gordinier,  McMurrich  and  Morris,  works 
published  by  them. 

Harris  E.  Santee. 


TABLE  OF  CONTENTS. 


CHAPTER  I. 
THE  MENINGES  OF  THE  BRAIN. 

PAGE 

Dura  Mater  of  the  Brain : i 

Structure  and  relations i 

Processes  i 

Sinuses 2-5 

Arachnoid  granulations  (Pacchioni) 5 

Arteries 6-7 

Nerves  7 

Contrasted  with  dura  of  spinal  cord 7 

Arachnoid  of  the  Brain : 8 

Structure   8 

Relations,  subarachnoid  spaces 8-9 

Vessels  and  nerves 9 

Contrasted  with  arachnoid  of  the  cord 9 

Pia  Mater  of  the  Brain : 9 

Structure  and  relations 9-10 

Chorioid  tela  of  third  and  fourth  ventricles 10 

Arteries  and  veins 10-13 

Nerves   13 

Contrasted  with  pia  of  spinal  cord 13 

Blood  Supply  of  the  Brain: 14-30 

Carotid  and  vertebral  arteries 14 

A.  Cerebral  Circulation,  Arteries : .''...  14-2 1 

Arterial  circle   (Willisi)  and  branches 14-15 

Ai.  Cortical  system  of  arteries 15-18 

Anterior  cerebral  arter}- 16 

Middle  cerebral  artery 16-1 7 

Posterior  cerebral  artery 17 

Chorioidal  arteries,  posterior  and  anterior 17-18 

A2.  Ganglionic  system  of  arteries 18-21 

vii 


Vni  TABLE    OF    CONTENTS. 

PAGE 

Antero-median  ganglionic  arteries i8 

Antero-lateral  ganglionic  arteries i8 

Postero-median  ganglionic  arteries 18-2.1 

Postero-lateral  ganglionic  arteries 21 

The  Veins  of  the  Cerebrum: 21-24 

Internal  veins  of  the  cerebrum 21 

Great  vein  of  the  cerebrum  (Galeni) 2 1-22 

External  veins  of  the  cerebrum 22-23 

Superior 22 

Medial 22-23 

Inferior 23 

Lymphatics  of  cerebrum 23-24 

B.  Circulation  of  the  Rhombencephalon: 24-30 

Bi.  The  medulla  oblongata 24 

B2.  The  pons  (Varolii) 24-27 

B3.  The  cerebellum 27-30 

Superior  cerebellar  artery 27-28 

Anterior  inferior  cerebellar  artery 29 

Posterior  inferior  cerebellar  artery 29 

Internal  cerebellar  veins. 29 

External  cerebellar  veins 29-30 

Superior 29 

Inferior 29-30 

Lymphatics  of  cerebellum 30 

Table  I.  Embryologic  Divisions  of  the  Brain 3'^~33 

Components  of  cerebrum 7,3 

Components  of  rhombencephalon 33 


CHAPTER  II. 

GENERAL  CONSIDERATION  OF  THE  BRAIN. 

Embryonic  Brain  Vesicles 34 

Their  cavities — the  ventricles 34 

Superior  view 34~35 

Posterior  view 35~3^ 

Inferior  view 36-41 

Anterior  area 36-37 

Middle  area 37-38 

Posterior  area : 38-41 


TABLE    OF    CONTENTS.  IX 

PAGE 

Roots  of  the  Twelve  Cerebral  Nerves: 42-49 

Nuclei,  genetic  and  terminal 42 

Olfactory  nerves 42 

Optic  nerve 42 

Oculo-motor  nerve 42-45 

Trochlear  nerve 45 

Trigeminal  nerve 45 

Abducent  nerve 45 

Facial  nerve 45-46 

Intermediate  nerve 45-4° 

Acustic  nerve 4" 

Glossopharyngeal  nerve 46 

Vagus  nerve 46-49 

Accessory  nerve 49 

Hypoglossal  nerve 49 


CHAPTER  in. 
THE  CEREBRUM. 

Subdivisions : 

End-brain 5° 

Inter-brain 5° 

Mid-brain 5° 

Section  I.  The  Fore-brain  or  Prosencephalon 50-144 

Exterior  surface  of  fore-brain 5  ^~9^ 

Definition  of  fissure  and  sulcus 52 

Subdivisions  and  borders 5^ 

Convex,  medial  and  basal 52 

Fissures  and  sulci  of  convex  surface 52-73 

Longitudinal  fissure  of  cerebrum 52-55 

Transverse  fissure  of  cerebrum 55 

Lateral  fissure  of  cerebrum  (Sylvii) 55-56 

Sulcus  centralis  (Rolandi) 56' 

Occipito-parietal  sulcus 56-59 

Lobes  and  gyri  of  convex  surface 59-73 

Frontal  lobe,  its  gyri  and  sulci 59-63 

Parietal  lobe,  its  gyri  and  sulci 63-67 

Occipital  lobe,  its  gyri  and  sulci 67-69 


TABLE    OF    CONTENTS. 


PAGE 


Temporal  lobe,  its  gyri  and  sulci 69-7 1 

Superior  surface 70 

External  surface 7o~7 1 

Island  (Reili),  its  sulci  and  gyri 71-73 

The  base  of  the  fore-brain 73-85 

Frontal  lobe,  inferior  surface 73~74 

Island  (Reili),  inferior  surface 74-77 

Rhinencephalon 77-79 

Olfactory  lobe 77-79 

Olfactory  bulb 77-78 

Olfactory  tract  and  striae 78 

Olfactory  triangle 79 

Parolfactory  area  (Brocae) 79 

Anterior  perforated  substance 79 

Tentorial  area  of  basal  surface 79-82 

Chorioidal    fissure 80 

Hippocampal  fissure 80 

Ectorhinal  sulcus , 80-81 

Fissura  coUateralis 81 

Inferior  temporal  sulcus 81 

Gyrus  fusiformis 81 

Gyrusjingualis 81 

Limbic  lobe,  inferior  part 81-82 

Gyrus  hippocampi  and  uncus 81-82 

Dentate  fascia 82 

Hypothalamus 82-85 

Pars  optica  hypothalami 82-84 

Lamina  cinerea  terminalis S^ 

Optic  chiasma,  nerves  and  tracts 83-84 

Tuber  cinereum  and  inf undibulum 84 

Hypophysis  (pituitary  body) 84 

Pars  mammillaris  hypothalami 82  and 84 

Corpora  mammillaria 84 

Fissures  and  sulci  of  medial  and  tentorial  surface 84-98 

Sulcus  cinguli   (calloso-marginal) 86 

Subparietal  sulcus 86 

Callosal  sulcus 86-89 

Occipito-parietal   sulcus 89 

Calcarine  fissure 89-90 

Hippocampal  fissure 90 


TABLE    OF    CONTENTS.  XI 

PAGE 

Chorioidal  fissure 90 

Collateral  fissure 90~93 

Ectorhinal  sulcus 90~93 

Inferior  temporal  sulcus 93 

Gyri  of  medial  and  tentorial  surface 93^98 

Gyrus  fornicatus 93~97 

Gyrus  cinguli 93^94 

Gyrus  hippocampi 94^97 

Uncus 94-97 

Lobus   pyraformis 97 

Limbic  lobe,  rhinencephalon 97 

Gyrus  rectus 97 

Gyrus  frontalis  superior  (g.  marginalis) 97 

Lobulus  paracentralis 97 

Praecuneus 97 

Cuneus    97 

Gyrus  lingualis 97 

Gyrus  fusiformis 97 

Summary  of  lobes  of  the  cerebrum 98 

Neopallium 98 

Rhinencephalon    (archipallium) 98 

Corpus  striatum 98 

Interior  surface  of  the  fore-brain 98-144 

Internal  capsule 99-104 

Inferior  lamina 99-100 

Motor  fibers 100 

Sensory  fibers 100 

Superior  lamina 100-104 

Genu,  frontal  and  occipital  parts 103 

Motor  fibers 103 

Common  sensory  fibers 103-104 

Special  sense  fibers 104 

Corpus  callosum: 104-108 

Upper  surface 107 

Gyri  supracallosus  and  subcallosus 107 

Inferior  surface 107 

Borders,  posterior  and  anterior 107-108 

Splenium,   rostrum,    genu,    truncus 108 

Boundaries  of  general  cavity  of  fore-brain 108-109 

Body  of  fornix 109 


Xll  TABLE    OF    CONTENTS. 

PAGE 

Crus  f ornicis no 

Columnae  f ornicis no 

Septum  pellucidum in 

Fifth  ventricle 111-112 

Lateral  ventricle  and  its  boundaries 11 2-1 2 7 

Central  part  (body) 1 12-120 

Corpus  striatum 115-119 

Lentiform  nucleus 116 

Nucleus  caudatus 116-119 

Stria  terminalis 119 

Thalamus 119 

Chorioid  plexus  of  lateral  ventricle 120 

Anterior  horn  of  the  lateral  ventricle 1 20-1 23 

Posterior  horn 123 

Inferior  horn 123-127 

Trigonum  coUaterale 124 

Hippocampus,  its  digitations 124 

Chorioid    epithelium , 124 

Third  Ventricle  and  Inter-Brain 127-144 

Posterior  commissure 132 

Roof  epithelium 132 

Pineal  body 132-135 

Chorioid  tela  of  third  ventricle 135-136 

Anterior  commissure 136-139 

Lamina  terminalis 139 

Thalamus 139-143 

Extremities — anterior  and  posterior 140 

Surfaces — medial,  superior,  lateral  and  inferior. .  140-143 

Tegmental  hypothalamic  region 143 

Nucleus  hypothalamicus  (Luysi) 143 

Lateral  geniculate  body 143 

Medial    geniculate    body 143-144 

Section  II.  The  Mid  Brain  (Mesencephalon): 144-164 

Surfaces — superior,  inferior,  anterior,  posterior 144-146 

Bases  pedunculi 147-151 

Intermediate  bundle 148 

Temporo-pontal  tract 148 

Pyramidal  tract 148-151 

Fronto-pontal  tract 15^ 


TABLE    OF    CONTENTS.  XUl 


PAGE 


Substantia  nigra 151 

Tegmenta 152-163 

Cerebral  aqueduct   (Sylvii) 152 

Nuclei  of  oculo-motor  and  trochlear  nerves 152-155 

Mesencephalic  nucleus  of  trigeminal  nerve 155 

Formatio-reticularis 155-163 

Tegmental  decussations 155 

Tracts  of  fibers  in  the  tegmentum 155-163 

Medial  (or  posterior)  longitudinal  bundle 155-158 

Anterior  longitudinal  bundle 158-159 

Fillet  or  lemniscus 159-161 

Medial  fillet — superior  fillet 159-160 

Lateral  fillet 160-161 

Spino-thalamic  tract 161-162 

Brachium  conjunctivum 162 

Rubro-spinal  tract 162 

Olivary  fasciculus 162 

Descending  root  of  trigeminal  nerve 163 

Quadrigeminal  lamina 163-164 

Colliculus  superior 163- 

Colliculus  inferior 163-164 

Brachium  superius 164 

Brachium  inferius 164 

Section  III.  Structure  of  the  Cerebrum: 164-241 

The  neurone  or  nerve  cell 167-173 

Cell-body,  perikaryon,  or  neurone  center 167 

Dendrites 167 

Axone 168 

Myelin  sheath 168 

Types  of  neurones  (three) 168 

Orders  of  neurones  (ist,  2d,  etc.) 168-171 

Functions  of  neurones 171 

Degeneration  of  neurones 1 71-172 

Development  of  neurones 172-173 

Sustentacular  tissue 173 

Epiblastic 1 73-1 74 

Neuroglia  and  ependyma 173-174 

Mesoblastic  connective  tissue 174 

Cortical  gray  matter 174-204 


XIV  TABLE    OF   CONTENTS. 


PACK 


Cortical  or  cerebral  localization 177-183 

Motor  area,  emissive 177 

Psychic  motor  area lyg 

Common  sensory  area 1 78 

Psychic  sensory  area lyg 

Acustic    center i3j 

Optic  center j3  j 

Olfactory  and  gustatory  centers 181 

Naming  center 181 

Centers  of  intonation,  equilibration  and  orientation  181 

Anterior  association  center,  abstract  conceptions 182 

Posterior  association  center,  concrete  conceptions 182-183 

Middle  association  center 183 

Cell  and  fiber  lamination 183-204 

Plexiform  layer 184-187 

Layer  of  small  pyramids 184  and  187 

Layer  of  medium-sized  pyramids 184  and  187 

External  layer  of  large  pyramids 184  and  187-188 

Layer  of  stellate  cells 184  and  188 

Internal  layer  of  large  pyramids 184  and  188-191 

Layer  of  fusiform  cells 184  and  191 

Radiations  of  Meynert 192 

Association  fibers  of  Meynert 192 

Atypical  cortex: 192-204 

Visual  cortex 192-195 

Olfactory  cortex 195-204 

Olfactory  bulb 195-196 

Uncus  hippocampi 196-199 

Nucleus  amygdalae 199 

Subiculum 199 

Fascia  dentata 200 

Trigonum  olfactorium,  etc 200-203 

Gyrus  cinguli 203 

Claustrum 204 

Ganglionar  gray  matter 204-22 1 

Corpus  striatum 204-208 

Centrifugal  fibers 207-208 

Centripetal  fibers 208 

Thalamus 208-217 

Thalamic  nuclei 208-21 1 


TABLE    OF    CONTENTS.  XV 

PAGE 

White  matter  of  the  thalamus 211-217 

Cortical   fillet 216-217 

Occipito-thalamic  radiation  (optic) 217 

Temporo-thalamic  radiation  (acustic) 217 

Red  nucleus 217 

Nucleus  hypothalamicus 218 

Metathalamus 218 

Lateral  geniculate  body 218 

Medial  geniculate  body 218-219 

Superior  colliculi  of  corpora  quadrigemina 219-220 

Anterior  longitudinal  bundle 2 19-220 

Inferior  colliculi  of  corpora  quadrigemina 220 

Nucleus  lateralis  superior 220 

Substantia  nigra 221 

Central  or  ventricular  gray  matter '. 22 1-224 

Hypothalamus 221-222 

Pars  optica 221 

Pars  mammillaris 221-222 

Massa  intermedia  (middle  commissure) 222 

Stratum  griseum  centrale  of  mid-brain 222-224 

Oculomotor  nucleus 223 

Trochlear  nucleus 223 

Trigeminal  nucleus  of  mid-brain 224 

Projection  fibers  of  the  cerebrum 224-234 

Corticifugal,  or  motor  fibers 225-231 

Intermediate  tract —  225 

Fronto-pontal  tract 225 

Tempora-pontal  tract 225-226 

Pyramidal  tract 226-231 

Head  and  neck  fibers 227 

Upper  extremity  fibers 228 

Trunk  fibers 228 

Lower  extremity  fibers 228-231 

I 


Destruction  of  by  clot,  etc 2 


Sensory  or  corticipetal  fibers 231-234 

Medial  fillet,  spino-thalamic  tract  and  brachium  con- 

functivum 231 

Olfactory  projection  fibers 232 

Cortical  fillet  (common  sensory) 232-233 

Taste  fibers  (not  located) 2^;^ 


XVI  TABLE    OF    CONTENTS. 

PAGE 

Auditory 233 

Lateral  fillet  and  brachium  inferius 233 

Temporo-thalamic  radiation 233 

Occipito-thalamic  radiation  (optic) 234 

Commissural  fibers  of  cerebrum 234-236 

Corpus  callosum 234 

Anterior  commissure 234-235 

Coramissura  hippocampi 236 

Association  fibers  of  cerebrum 236-241 

Short  association  fibers 236-238 

Long  association  fibers 238-241 

Cingulum  of  gyrus  fornicatus 238 

Fornix    238-240 

Uncinate  fasciculus 240 

Superior  longitudinal  fasciculus 240 

Inferior  longitudinal  fasciculus 240-241 

Fasciculus  occipito-frontalis 241 

Perpendicular  fasciculus 241 


CHAPTER  IV. 

THE  RHOMBENCEPHALON. 

Section  I.  The  Cerebellum: 242-266 

Function 242 

Divisions: 242 

Cerebellar  hemispheres 242-243 

Vermis  cerebelli  or  worm 243 

Cerebellar  notches,  anterior  and  posterior 244 

Medullary  Body : 244-247 

Inferior  medullary  velum 244 

Brachia  conjunctiva 245 

Superior  medullary  velum  (Vieussensi) 246 

Corpora  restiforraia 246-247 

Brachia  pontis 247 

Horizontal  sulcus  of  cerebellum 247-248 

Superior  Surface  of  Cerebellum: 248-251 

Sulci  of  upper  surface 248-249 

Precentral  sulcus 248 

Postcentral  sulcus 249 


TABLE    OF    CONTENTS.  XVU 


PAGE 


Predeclivil  sulcus 249 

Postdeclivil  sulcus 249 

Lobes  of  superior  surface 250-251 

Lobus  lingulas 250 

Lobus  centralis 250 

Lobus  culminis  monticuli 250 

Lobus  declivis  monticuli 251 

Lobus  folii  vermis 251 

Inferior  Surface  of  Cerebellum: 251-256 

Sulci  of  lower  surface 252-253 

Postnodular  sulcus 252 

Prepyramidal  sulcus 252-253 

Postpyramidal  sulcus 253 

Midgracile  and  postgracile 253 

Lobes  of  lower  surface 253-256 

Lobus  noduli 253-254 

Lobus  uvulae 254 

Lobus  pyramidis 254-255 

Lobus  tuberis 255-256 

Cortical  Gray  Matter  of  the  Cerebellum 256-260 

Superficial  layer 256-258 

Stratum  cinereum 256 

Stratum  gangliosum 257 

Cells  of  Purkinje  and  stellate  cells 257 

Fibers  of  superficial  layer 257-258 

Deep  layer  (stratum  granulosum) 258-260 

Cells  of  granular  layer 258-259 

Fibers  of  granular  layer 260 

Function  of  stellate,  granule  and  Purkinje  cells 260 

Neuroglia  of  cerebellum 260 

Ganglionar  Gray  Matter  of  Cerebellum 260-262 

Function,  relay  stations 260 

Nucleus  dentatus 260-261 

Nn.  emboliformis,  globosus  and  fastigii 261 

White  Substance — Corpus  Medullare: 262-266 

Projection  fibers 263-265 

Brachium  conjunctivum 263 

Superior  medullary  velum 263-264 

Brachium  pontis 264 

Corpus  restiforme 264-265 


XVlll  TABLE    OF    CONTENTS. 

PAGE 

Commissural  fibers 265 

Association  fibers 265-266 

Section  II.    The  Pons  (Varolh) 266-284 

Surfaces : 266-270 

Superior  and  inferior 266 

Anterior  (Tuber  annulare) 266-269 

Posterior — ^ventricular,  and  attached  part 269-270 

Transverse  fibers  of  the  pons 271-272 

Superficial  of  pars  basilaris  pontis 271 

Deep  transverse  of  pars  basilaris  pontis 271 

Transverse  of  pars  dorsalis  pontis 271-272 

Trapezoid  body 272 

Longitudinal  fibers  of  the  pons 272-278 

Ventral 272 

Dorsal 272-278 

Medial  fillet  and  superior  fillet 273-274 

Lateral  fillet 272 

Spino-thalamic  tract 272 

Ascending  anterior  cerebello-spinal  tract 272-276 

Gowers's  tract 276 

Medial  longitudinal  bundle 276 

Anterior  longitudinal  bundle 276 

Rubro-spinal    tract 276-277 

Olivary  bundle 277 

Descending  root  of  trigeminal  nerve 277 

Spinal  tract  n.  trigemini 277 

Gray  Matter  of  the  pons 277-284 

Nucleus  pontis 277 

Stratum  nucleare /. 278-284 

Superior  olivary  nucleus 278-279 

N.  prasolivaris  and  n.  semilunaris 279 

Nucleus  of  trapezoid  body 279 

Nuclei  of  recticular  formation 279-280 

Ponto-spinal  tracts  (Collieri) 280 

Nuclei  of  trigeminal  nerve 281 

Genetic  (motor) 281 

Terminal  (sensory) 281 

Nucleus  of  abducent  nerve 281-282 

Nucleus  of  facial  nerve 282 


TABLE    OF    CONTENTS.  XIX 

PAGE 

Salivary  nucleus 283 

Vestibular  nucleus  of  auditory 283 

Lesions  in  pons 283 

Section  III.    Medulla  Oblongata  (Myelencephalon)  . .  284-313 

Origin 285 

Ventricle 285 

Surfaces 286-290 

Anterior  lateral  sulcus 286 

Posterior  lateral  sulcus 286 

Anterior    surface 286-287 

Lateral  surface 287-288 

Olive 287 

Lateral  column 287-288 

Posterior  surface 288-290 

Restiform  body 288 

Roof  epithelium  of  fourth  ventricle 289 

Floor  of  fourth  ventricle 290 

White  matter  of  medulla 290-302 

Substantia'  reticularis 291 

Raphe 291 

Transverse  fibers 291-292 

Pyramidal  decussation 291 

Arcuate  fibers,  external  and  internal 291-292 

Fillet  decussation 292 

Cerebello-olivary  fibers 292 

Dorso-ventral  fibers 292-293 

Anterior  external  arcuate 292 

Roots  of  eighth  to  twelfth  cerebral  nerves 293 

Longitudinal  fibers  of  anterior  area: 293-298 

Pyramid,  anterior  and  lateral  tracts 294 

Medial  fillet  (interolivary  stage) 295 

Medial  longitudinal  bundle  (posterior) 296 

Anterior  longitudinal  bundle 297 

Longitudinal  fibers  of  lateral  area 298-300 

Fasciculus  lateralis  proprius 298 

Descending  anterior  cerebello-spinal  tract 298 

Ascending  anterior  cerebello-spinal  tract 299 

Rubro-spinal  tract 300 

Longitudinal  fibers  of  posterior  area 300-302 


XX  TABLE    OF    CONTENTS. 

PAGE 

Funiculus  gracilis 300 

Funiculus  cuneatus 300 

Spinal  tract  of  trigeminal  nerve 301 

(Posterior)  Cerebello-spinal  tract 301 

Restiform  body 301 

Vestibular  and  cochlear  nuclei 302 

Tractus  solitarius 302 

Gray  matter  of  the  medulla 302-3 13 

Nucleus  of  external  arcuate  fibers 302 

Nuclei  in  floor  of  ventricle  (s.  nucleare) 303-310 

Hypoglossal  nucleus 303 

Nucleus  lateralis  inferior 303-304 

Nucleus  ambiguus 303-304 

Nuclei  alse  cincerese 304  and  306 

Nucleus  tractus  solitarii 306 

Nucleus  tractus  spinalis  n.  trigemini 306 

Vestibular  nuclei 307-308 

Cochlear  nuclei 309-3 10 

Special  nuclei  in  medulla 3 10-3 13 

Nucleus  funiculi  gracilis 3 10-3 1 1 

Nucleus  funiculi  cuneati 3t^'^~3 i i 

Nucleus  olivaris  inferior 312 

Section  IV.    The  Fourth  Ventricle 313-325 

Boundaries 313-314 

Floor  of  fourth  ventricle 314-318 

Colliculus  facialis 317 

Fovea  superior 317 

Locus  caeruleus 317 

Hypoglossal  triangle 317 

Ala  cinerea  (trigonum  vagi) 317 

Area  acustica 320 

Origin  of  cerebral  nerves 320-325 

Table  II.  Sensory  Nerves  and  Roots 320-321 

Table  III.  Motor  Nerves  and  Roots 321-322 

Terminal  nuclei 322-324 

Common  sensory 322 

Cortical  and  reflex  connections —  322 

Special  sense 322-324 

Cortical  and  reflex  connections 324 


TABLE    OF    CONTENTS.  XXI 

PAGE 

Genetic  nuclei 324-325 

Cortical  and  reflex  connections 324-325 

CHAPTER  V. 

MEMBRANES  OF  THE  SPINAL  CORD. 

Dura  mater 326 

Arachnoid   326-329 

Pia  mater 329-330 

Blood  Supply  of  the  Spinal  Cord: 33'^''33^ 

Spinal  arteries,  anterior  and  posterior 33°~33^ 

Fissural  or  centrifugal 331 

Centripetal 33'^~33^ 

Venas  spinales  internee 332 

Root  and  fissural  veins 332 

Venae  spinales  externa^ 332 

Internal  vertebral  plexus 332 

Lymphatics 332 

CHAPTER  VI. 

THE  SPINAL  CORD. 

Extent ^^^ 

Diameters 333-335 

Cervical  enlargement 333~334 

Lumbar  enlargement 334~335 

Sixth  ventricle  (canalis  centralis  spinalis) 337 

Fissures  of  the  cord: 337~338 

Anterior  median  fissure 337 

Posterior  median  fissure 337 

Posterior  lateral  sulcus 337~338 

Anterior  root-line   (s.  lateralis  anterior) 338 

Posterior  intermediate  sulcus ^^8 

I.  Gray  Matter  of  the  Cord: 33S~35i 

H-shaped  column 339 

Substantia  gelatinosa 339 

Substantia  spongiosa 339 

Gray  crescent 339~349 

Anterior  colunina 339-344 

Cells  of  anterior  columna 340-344 


XXU  TABLE    OF   CONTENTS. 

PAGE 

Golgi  cells 340 

Deiters  cells 340 

Medial  column 340 

Lateral  column 340,  343-344 

Cortical  connection " 343 

Reflex  mechanism 343-344 

Lesions  of  anterior  columna 344 

Center  of  crescent  and  columna  lateralis 344-347 

Intermedio-lateral    column   of    cell-bodies    (efferent 

sympathetic  neurones) 344-347 

Posterior  columna 347-349 

Neurones  of  head  of  posterior  columna 347-348 

Nucleus  dorsalis  (Clarki)  terminal  nucleus  of  sym- 
pathetic)    348-349 

Gray  commissure  of  spinal  cord 350 

Gray  anterior  commissure 350 

Posterior  commissure 350 

Lesions  of  gray  substance , 350 

2.  White  Matter  of  the  Spinal  Cord: 351-362 

Transverse  fibers 351 

White  anterior  commissure 351 

Dorso-ventral  fibers 35-~352 

Longitudinal  fibers 352 

Funiculus  anterior 352 

Funiculus  lateralis 352 

Funiculus  posterior 352 

•Ascending  tracts 352 

Descendihg  tracts 352 

Mixed  tracts 352 

Embryological  method  of  locating  tracts 352-353 

Pathological  and  experimental  method 353 

Tracts  of  the  Spinal  Cord 354-362 

Antero-lateral  fasciculus  proprius 354 

Medial  longitudinal  bundle 354 

Anterior  pyramidal  tract 355 

Anterior  longitudinal  bundle 355 

Descending  anterior  cerebello-spinal  tract 356 

Ascending  anterior  cerebello-spinal  tract 35^-357 

Spino-thalamic  tract 35^-357 

Triangular  tract  of  Helwig 357 


TABLE    OF    CONTENTS.  XXlll 

PAGE 

(Posterior)  Cerebello-spinal  tract 357~358 

Spino-vestibular  tract 357-358 

Lateral  pyramidal  tract 358 

Rubro-spinal  tract 358 

Lesions  of  anterior  and  lateral  funiculi 359 

Marginal  tract  (Lissaueri) 359 

Entry  zone 359-360 

Fasciculus  gracilis  (Golli) 360-361 

Fasciculus  cuneatus  (Burdachij 361 

Descending  tracts  from  posterior  roots 361 

Descending  postero-medial  tract  (comma,  oval,  septo- 
marginal and  median  triangular  tract) 361 

Descending  posterolateral  tract 362 

Posterior  fasciculus  proprius 362 

Cornu-commissural  tract ' 362 

Lesions  of  posterior  columns 362 

Roots  of  the  spinal  nerves 362-365 

Anterior  root 363 

Apparent  origin 363 

Real  origin   (genetic  nuclei) 363 

Voluntary  motor  fibers 363 

Sympathetic  efferent  fibers 363 

Lesions 360-364 

Posterior  root 364-365 

Spinal  ganglion  (origin) 364 

Apparent  central  termination 364 

Real  central  termination,  terminal  nuclei 364 

Gray  matter  of  the  cord 364-365 

Nuclei  of  medulla  oblongata 365 

Physiological  groups  of  posterior  root-fibers 365 

Lesions  of  posterior  roots 365 

CHAPTER  VIL 
TRACING  OF  IMPULSES. 

Efferent,  or  Motor  Paths-: 366-374 

Cerebro-spinal  or  pyramidal  paths 366-369 

Through  spinal  nerves 366 

Through  cerebral  nerves 369 

Cerebro-pontal  paths 369-370 

Fronto-pontal 370 


XXIV  TABLE    OF    CONTENTS. 


PAGE 


Temporo-pontal , 370 

Intermediate 370 

Spinal  and  cerebral 370 

Paths  through  red  nucleus 37o~373 

Rubro-spinal  path,  direct 370-373 

-    Indirect  via  brachium  conjunctivum 373 

Ponto-spinal  paths  (CoUieri) 373 

Medial  ponto-spinal  tract 373 

Lateral  ponto-spinal  tract 373 

Short  fiber  paths  in  f or matio -reticularis 373-374 

II.  Afferent,  or  Sensory  Paths,   General  Sensations: 377-383 

Tactile,  muscular,  pain,  and  temperature  sense 377 

(I).  Muscular  and  tactile  impulses  from  muscles,  skin, 

etc 377-381 

Through  fasciculi  gracilis  et  cuneati 377-378 

Direct  route 378 

Indirect  route 378 

Through  cerebral  nerves  and  medial  fillet.. 378-381 

(II).  Muscular  and  tactile  impulses  from  viscera 381 

Through  posterior  cerebello-spinal  tract 381 

(III).  Paths  for  pain,  temperature  and  tactile  impulses  . .  381-382 

Through-  spino-thalamic  tract 381-382 

Through  ascending  anterior  cerebello-spinal  tract 381-382 

Through  cerebral  nerves  and  spino-thalamic  tract 382 

Short  fiber  paths 382-383 

Afferent  Paths — Special  Sensations: 383-390 

Olfactory  path 383-384 

Optic  path 384-385 

Auditory  path 385-389 

Cochlear  (hearing  proper) 386 

Vestibular  (equilibrium) 386-389 

Reflex  connections 389 

Gustatory  path 389 

Lesions  of  special  sense  paths 389-390 

III.  Reflex  Paths : 390-394 

Reflex  arcs 390 

(i)  Spinal  reflexes 390-392 

Coordinating  reflexes 390 

Defecation  reflexes 391-392 

(2)  Cerebral  reflexes 392-393 


TABLE    OF    CONTENTS.  XXV 


PAGE 


(3)  Spino-cerebral  reflexes 393 

(4)  Cerebro-spinal  reflexes 393~394 

Respiratory  reflexes 393 

Equilibrium  reflexes 393 

Pupillary  reflexes 394 

CHAPTER  VIII. 

EMBRYOLOGY  OF  THE  BRAIN  AND  SPINAL  CORD. 

Medullary  plate  and  ridges 395 

Neural  Tube: 395-400 

Brain  vesicles 395  and  402 

Ependymal  cells 397 

Indifferent  cells 397~398 

Neuroblasts,  neurones 398 

Spongioblasts,  neuroglia 398~399 

Zones,  roof -plate  and  floor-plate 399-400 

Neural  Crest : 400-401 

Cephalic   portion 400 

Cerebral  nerve  ganglia 400 

Unipolar  and  bipolar  neurones 400-401 

Spinal  portion  of  crest 401 

The  Brain: 401-426 

Flexures 402 

Table  IV.  Brain  Vesicles  and  Derivatives 403 

Table  V.  Secondary  Brain  Vesicles 403-404 

Telencephalon  (end-brain) 404-415 

Table  VI.  Derivatives  of 404-405 

Optic  vesicle,  cup  and  retina 405 

Hemisphere  of  cerebrum 405-415 

Rhinencephalon 406-409 

Primary  fissures 409-410 

Secondary  sulci  and  fissure 410-41 1 

Transverse  fissure  of  cerebrum .^ 411 

Cerebral  cortex  and  medulla 41 1-41 2 

Fornix 412 

Stria  terminalis 412 

Internal  capsule 412-413 

Anterior  commissure 413-414 

Corpus  callosum 414 


XXVI  TABLE    or    CONTENTS. 

PAGE 

Septum  pellucidum '. .  415 

Pars  optica  hypothalami 415 

Diencephalon  (inter-brain) 415-417 

Table  VII.  Derivatives  of 415 

Roof -plate 416 

Dorsal  lamina 417 

Ventral  lamina  and  floor-plate 417 

Mesencephalon  (mid-brain) 417-418 

Table  VIII.  Derivatives  of 417-418 

Metencephalon  (hind-brain) 418-424 

Table  IX.  Derivatives  of 419 

Cerebellum 418-42 1 

Vermis  and  hemispheria 419-420 

Sulci 420-421 

Cortex  and  ganglia 421 

Corpus  restiforme  and  brachia 42 1 

Pons  (Varolii) 42 1-422 

Myelencephalon  (medulla  oblongata) 422-426 

Internal  surface 423 

External  surface 423-424 

Table  X.  Derivatives  of  Myelencephalon 424 

Ependymal  layer 424-425 

Mantle  layer 425 

Neuroglia  layer,  marginal  velum 425-426 

The  Spinal  Cord: 426-430 

Ventriculus  terminalis 426 

Filum  terminale 426 

Cauda  equina 426 

Meninges 426 

Zones,  ventral  and  dorsal 426-427 

Histologic  layers 427-428 

Marginal  velum,  neuroglia  layer 428 

Mantle  layer ' 428-429 

Ependymal  layer 429 

Longitudinal  tracts 429-430 

Order  of  meduUation 429-430 

Fissures  of  cord 430 

Posterior  median  fissure 430 

Posterior  lateral  sulcus 43° 

Anterior  median  fissure 430 


LIST  OF  ILLUSTRATIONS 


FIG.  PAGE 

1.  Sagittal  section  of  skull,  showing  falx  cerebri,  falx  cerebelli, 

a  part  of  the  tentorium  cerebelli  and  the  sinuses  of  the 
dura  mater.     (After  Morris's  Anatomy) 3 

2.  Upper  surface  of  tentorium  cerebelli,  tentorial  notch  and  cer- 

tain sinuses  of  the  dura.     (After  Morris's  Anatomy) . .       4 

3.  Sinuses  of  the  dura  mater  in  the  base  of  cranium,  etc.     (After 

Morris's  Anato?ny) 5 

4.  Coronal  section  of  meninges  showing  falx  cerebri,  superior 

sagittal  sinus  and  the  arachnoid  granulations.     (Gor- 
dinier  after  Key  and  Retzius) 6 

5.  Middle  meningeal   artery  inside  the  cranium.     (After  Mor- 

ris's Anatomy) 7 

6.  Diagram  of  pia  mater  and  arachnoid,  showing  subarachnoid 

spaces.     (After  Morris's  Anatomy) 9 

7.  Horizontal  section  of  the  cerebrum.     Fornix  turned  back  to 

show  the  chorioid  tela  of  third  ventricle.     {Original).     11 

8.  Roof  and  lateral  walls  of  fourth  yentricle  and  its  chorioid 

plexus.     (After  Morris's  Anatomy) 13 

9.  Arterial  circle  of  Willis  and  its  branches.     The  base  of  the 

brain.     (After  Morris's  Anatomy) 15 

10.  Arterial  circle  (Willisi)  and  base  of  the  cerebrum.     (After 

Gordinier  from  Quain) 19 

11.  Middle  cerebral  artery,  and  its  branches.     (After  Gordinier 

from  Quain) 22 

12    Anterior  and  posterior  cerebral  arteries.     (After  Spaltehoh). .  25 

13.  Arteries  of  the  medulla  oblongata.     {Gordinier  after  Buret) ...  27 

14.  Median  section  of  embryonic  brain  of  third  month.     (After 

McMurrich  from  His) 28 

15.  Divisions  of  the  brain,  diagrammatic.     (After  Morris's  Anat- 

omy)      31 

16.  Neural  tube  and  brain  vesicles.     (After  Morris's  Anatomy). .     35 

17.  Diagrammatic  horizontal  section  of  vertebrate  brain,  showing 

vesicles  and  ventricles.     (After  Morris  from  Huxley)     36 
xxvii 


XXVlll  LIST    OF    ILLUSTRATIONS. 

FIG.  PAGE 

i8.  Diagrammatic  median  section  of  vertebrate  brain  showing 
vesicles,  ventricles  and  olfactory  diverticulum.  (After 
Morris  from  Huxley) 37 

19.  Antero-superior  surface  of  the  brain.     (Original) 39 

20.  The  posterior  aspect  of  the  brain.     (Original) 43 

21.  The  base  of  brain.     (Original) 47 

22.  Latero-superior  aspect  of  the  brain,  showing  great  fissures, 

lobes,  poles  and  borders.     (Original) 53 

23.  The  convex  surface  of  the  cerebrum,  showing  the  fissures  and 

sulci.     (Original) 57 

24.  Gyri  of  the  convex  surface  of  the  cerebrum.     (Original) 61 

25.  Lateral  aspect  of  the  brain.    Part  of  frontal  and  parietal  lobes 

are  cut  away  to  show  the  island  (Reili)  and  the  superior 
surface  of  the  temporal  lobe,  arachnoid  granulations, 
etc.    (Original) 65 

26.  Base  of  the  fore-brain  and  cut  surface  of  mid-brain.     Right 

temporal  pole  is  cut  away.     (Original) 75 

27.  The  median  section  of  the  brain.     (Original) 87 

28.  Medial  surface  of  left  cerebral  hemisphere,  showing  lobes  and 

sulci.     (Original) 91 

29.  Gyri  on  medial  surface  of  hemisphere.     (Original) 95 

30.  Transverse  "section  of  the  brain,  directed  from  the  pons  ob- 

liquely upward  and  forward,  showing  internal  capsule, 
corpus  callosum,  ganglia  and  ventricles  of  the  fore- 
brain.     (Original) loi 

3 1 .  Horizontal  section  of  right  cerebral  hemisphere  cutting  corpus 

callosum,  internal  capsule,  corpus  striatum,  thalamus, 
and  the  island.     (Original) 105 

32.  Sagittal  section  of  basal  part  of  right  cerebral  hemisphere 

showing  inferior  lamina  of  internal  capsule,  hippocam- 
pus, inferior  horn  of  lateral  ventricle.     (Original) 113 

^^.  Diagram  of  internal  capsule  in  colors.     (Original) 115 

34.  Dorsal  surface  of  corpus  callosum,  cerebral  hemisphere  cut 

away  to  expose  it.     (Original) 117 

35.  Horizontal  section  of  cerebrum,  cutting  splenium  and  genu  of 

corpus  callosum,  showing  lateral  ventricles,  septum  pel- 
lucidum,  fornix  and  transverse  temporal  gyri.  (Orig- 
inal)     121 

36.  Horizontal  section  of  cerebrum  just  below  splenium  of  corpus 

callosum,  showing  commissura  hippocampi,  fornix,  sep- 


LIST    OF    ILLUSTRATIONS  XXIX 

FIG.  PAGE 

turn  pellucidum,  the  island  and  lateral  ventricles.  (Or- 
iginal)      125 

37.  Horizontal  section  of  cerebrum.     Fornix  turned  back,  showing 

chorioid  tael  of  third  ventricle,  and  internal  cerebral 
veins.     (Original) 129 

38.  Transverse  section  of  left  cerebral  hemisphere  cutting  the 

splenium  and  showing  the  posterior  horn  and  the  floor 
of  the  inferior  horn  of  the  lateral  ventricle.     (Original)  1 3 1 

39.  The  inferior  and  posterior  horns  of  the  lateral  ventricle,  shown 

by  removal  of  their  lateral  walls.     (Original) i^2) 

40.  Horizontal  section  of  cerebrum  through  genu  and  below  sple- 

nium of  corpus  callosum,  fornix  and  chorioid  tela  turned 
back,  to  show  inter-brain  and  third  ventricle.  (Or- 
iginal)     137 

41.  Lateral   and   dorsal  view  of  the  ventricles.     Diagrammatic. 

(Original) : 141 

42.  Transverse  section  of  brain,   cutting  corpora  mammillaria. 

(After  Told.  Morris's  Anatomy) 145 

43.  The  region  of  the  mid-brain  showing  pulvinar  of  the  thalamus, 

the  geniculate  bodies,  the  corpora  quadrigemina  and 
brachia,  the  pineal  body,  the  optic  tract  and  the  fourth 
nerve.     (Origind) 147 

44.  The  dorsal  or  posterior  aspect  of  the  inter-brain,  the  mid-brain, 

the  pons  and  the  medulla.     (Original) 149 

45.  Anterior  aspect  of  the  mid-brain,  pons,  and  medulla.     (Orig- 

inal)     153 

46.  Transverse  section  through  the  corpora  mammillaria  and  the 

superior  coUiculi  of  the  corpora  quadrigemina.  -(Orig- 
inal)      157 

47.  Section  of  the  mid-brain  through  superior  colliculi  and  the  ap- 

parent origin  of  the  oculo-motor  nerve.     (Original)  ..   159 

48.  Section  of  the  mid-brain  cutting  the  inferior  colliculi  of  the  cor- 

pora  quadrigemina,     (Original) 161 

49.  Varieties  of  neurones  in  the  human  nervous  system.     (After 

Morris's  Anatomy) 165 

50.  Motor  neurone,     (After  Barker's  Nervous  System) 169 

51.  An  efferent  neurone  and  an  afferent  neurone.     (After  Bru- 

baker's  Physiology) 171 

52.  Diagram  showing  development  of  neurones  in  the  spinal  cord. 

(McMurrich  after  Schdffer) 172 


XXX  LIST    OF    ILLUSTRATTONS. 

FIG.  PAGE 

53.  Neuroglia  cells  and  ependyma  cells  of  the  spinal  cord.     (After 

Lenhossek,  Gordinier's  Nervous  System) 173 

54.  Cortical  areas  on  convex  surface  of  cerebral  hemisphere.     (Or- 

iginal)     175 

55.  Cortical  areas  on  the  medial  and  tentorial  surface  of  the  cere- 

bral hemisphere.     (Original) 179 

56.  Cortical  areas  after  C.  K.  Mills.     Convex  surface  of  cerebral 

hemisphere. .    (Brubaker's  Physiology) 182 

57.  Cortical  areas  after  C.  K.  Mills.     Medial  and  tentorial  surface 

of  cerebral  hemisphere.     (Bncbaker's  Physiology) 183 

58.  Cell  and  fiber  lamination  in  the  posterior  half  of  the  anterior 

central  gyrus.  The  motor  area.  (After  A.  W.  Camp- 
hell) 185 

59.  Cell  and  fiber  lamination  in  the  anterior  half  of  the  posterior 

central  gyrus.  The  common  sensory  area.  (After 
A.  W.  Campbell) 189 

60.  Cell  and  fiber  lamination  in  the  calcarine  region.    Receptive 

visual  area.     (After  A.  W.  Campbell) 193 

61.  Cell  and  fiber  lamination  in  the  uncus  hippocampi  (lobus  pyra- 

formis).     The  area  of  smell.     (Aiter  A.  W.  Campbell)  197 

62.  Transverse  section  of  the  hippocampal  region.   (Aitev  Edinger)  201 

63.  Chief  elements  of  the  olfactory  bulb.     (Gordinier  after  Van 

Gehtichten)   203 

64.  Horizontal  section  of  the  cerebrum  through  genu  and  below 

splenium  of  corpus  callosum,  fornix  and  chorioid  tela 
turned  back  to  show  inter-brain  and  third  ventricle. 
(Original) 205 

65.  Dissection  of  brain  to  show  geniculate  bodies,  optic  tract, 

nucleus  amygdalae,  etc.     (After  Morris's  Anatomy) 207 

66.  Transverse  section  of  the  brain  in  the  line  of  the  pyramidal 

tracts,  showing  basal  ganglia,  internal  capsules,  corpus 
callosum,  lateral  and  third  ventricles,  etc.  Viewed 
from  front.     (Morris's  Anatomy  after  Toldt) 209 

67.  The  optic  path.     (Original) 213 

68.  Section  of  mid-brain  through  superior  coUiculi  and  the  appa- 

rent origin  of  the  oculomotor  nerve.     (Original) 215 

69.  Section  of  the  mid-brain  cutting  the  inferior  colliculi  of  the  cor- 

pora  quadrigemina.     (Original) 216 

70.  Horizontal  and  sagittal  section  through  internal  capsule,  much 

enlarged.     (Original) 226 


LIST    OF   ILLUSTRATIONS.  XXXI 

FIG.  PAGE 

71.  Diagram  of  internal  capsule  in  colors.     {Original) 227 

72.  A  diagram  showing  motor  and   sensory  paths,   motor  red, 

sensory  blue.  (After  Gordinier's  Central  Nervous 
System) 229 

73.  Transverse   section   of   cerebrum,   cutting  corpus   callosum, 

anterior  commissure  and  optic  chiasma.  Viewed  from 
front.  Commissural  fibers.  {Morris's  Anatomy  after 
Toldt) 235 

74.  Diagram  of  association  fibers  in  the  cerebral  hemisphere. 

{Gordinier  and  Quain  after  Meynert) 237 

75.  Fasciculus  occipito-frontalis.     Stria  terminalis  and  fasiculus 

imcinatus.     {Gordinier  after  Dejerine) 239 

76.  Dorsal  view  of  inter-brain,  mid-brain  and  cerebellum.     Su- 

perior surface  of  cerebellum.     {Original) 243 

77.  Anterior  aspect  of  cerebellum.     {Original) 245 

78.  Dissection  of  rhombencephalon  to  show  brachium  conjuncti- 

vum,  brachium  pontis  and  corpus'  restiforme.  (Gor- 
dinier, Sappey  after  Hirschjeld  and  Leveille) 246 

79.  Median  section  of  cerebellum,  pons  and  medulla.     {Original)  247 

80.  Inferior  surface  of  cerebellum.     {Original) ■ 252 

81.  Sagittal  section  of  cerebellum,  cutting  nucleus  dentatus.     (Or- 

iginal)     255 

82.  Section  of  cerebellar  gyrus  made  parallel  with  its  free  border. 

Diagrammatic.     (Cunningham  after  Kblliker) 258 

83.  Section  across  a  cerebellar  gyrus  at  a  right  angle  to  the  free 

border.  Diagrammatic.  (Gordinier  after  Van  GeJnich- 
ten) 259 

84.  Horizontal  section  of  cerebellum  cutting  nuclei  and  brachia 

conjunctiva.     (Morris's  Anatomy  after  Toldt) 261 

85.  Anterior   aspect   of   mid-brain,   pons   and    medulla.     (After 

Morris's  Anatomy) 267 

86.  Dorsal   surface  of  pons  and   medulla.     (Morris's  Anatomy 

modified  from  Spaltehoh) 270 

87.  Superior  transverse  section  of  the  pons.     (Original) 275 

88.  Inferior  transverse  section  of  the  pons  together  with  the  cere- 

bellum.    (Original) 277 

89.  Diagram  of  the  auditory  paths  in  the  pons.     (After  Morris's 

Anatomy) 280 

90.  Section  of  embyronic  medulla,  embryo  measuring  9.1  mm.  in 

length.     (Gordinier  and  Minot  after  His) 285 


XXXll  LIST    OF    ILLUSTRATIONS. 

FIG.  PAGE 

91.  Roof  and  lateral  walls  of  fourth  ventricle,  and  its  chorioid 

plexuses.     (After  Morris's  Anatomy) 289 

92.  Section  of  medulla  oblongata  near  the  pons.     (Original) 295 

93.  Section  of  the  medulla  oblongata  at  the  middle  of  olive.     (Or- 

iginal)     297 

94.  Section  of  the  medulla  oblongata  at  the  fillet  decussation.   (Or- 

iginal)    305 

95.  Section  of  the  medulla  oblongata  at  the  pyramidal  decussation. 

(Original) 311 

96.  Nuclei  of  the  cerebral  nerves  in  the  medulla,  pons,  mid-brain, 

inter-brain,  and  olfactory  bulb.  Motor  (or  genetic) 
nuclei  red,  terminal  (or  sensory)  nuclei  blue.  (After 
Morris's   Anatomy)    315 

97.  Meninges  of  the  spinal  cord.     A,  Transverse  section.    (After 

Key  and  Retzius.)  B.  Anterior  view.  (After  Ellis.) 
(Morris's  Anatomy) 327 

98.  Diagrammatic  section  of  the  spinal  meninges  and  spinal  cord. 

(After  Morris's  Anatomy) 329 

99.  The  arteries  and  veins  in  the  spinal  cord.     Diagrammatic. 

(After  Morris's  Anatomy) 331 

100.  Posterior  view  of  the  spinal  cord,  the  dura  mater  and  the  arach- 
noid being  laid  open  and  turned  aside.     (Bruhaker 

after    Sappey) 334 

loi.  Sections  of  the  spinal  cord :  A.  The  cervical.  B.  The  thora- 
cic. C.  The  lumbar,  and  D.  The  lower  sacral.  (Or- 
iginal)    335 

102.  Tracts  of  fibers  and  columns  of  cells,  in  the  cervical  and  thora- 

cic regions  of  the  cord.  Diagrammatic.  (In  part  after 
Bruce  and  Cunningham) 341 

103.  Tracts  of  fibers  and  columns  of  cells  in  the  lumbar  and  sacral 

regions  of  the  cord.  Diagrammatic.  (In  part  after 
Bruce  and  Cunningham) 345 

104.  The  roots  of  the  spinal  nerves.     Diagrammatic.     (Original) .  349 

105.  Direct  motor  paths  from  cerebral  cortex,  to  cerebral  and  spi- 

nal nerve.     Diagrammatic.     (Original) 367 

106.  Indirect  motor  paths  to  the  spinal  nerv^es.     Diagrammatic. 

(Original) 371 

107.  Common  sensory  paths,  muscular  and  tactile,  by  way  of  the 

posterior  column  and  (posterior)  cerebello-spinal  tract. 
Diagrammatic.     (Original) 375 


LIST    OF    ILLUSTRATIONS.  XXXlll 

FIG.  PAGE 

io8.  Common  sensory  paths,  pain,  temperature  and  touch,  by  way 
of  ascending  anterior  cerebello-spinal  and  spino-thala- 
mic  tracts.     Diagrammatic.     (Original) 379 

109.  Chief  elements  of  the  olfactory  bulb.     (Gordinier  after  Van 

.    Gehuchten)   384 

no.  The  chief  retinal  elements.     (Aittr  Bmbaker's  Physiology). .   385 

111.  The  optic  path.     (Original) 387 

112.  A    simple    spinal    reflex  arc.      {Bruhaker  after  Marat  and 

Dayon) 391 

113.  A  more  complicated  spinal  reflex  arc,  involving  the  fasciculi 

proprii.     (Brubaker  after  Kolliker) 392 

114.  Medullary  groove,  neural  tube,  etc.     [Gordinier  after  E.  A. 

Schdjer) 396 

115.  Two  histologic  layers  in  the  embryonic  spinal  cord,  embryo 

4.25  mm.  long.    (McMurrich  after  His) 397 

116.  Diagram  showing  development  of  neurones  in  the  spinal  cord. 

(McMurrich  after  Schdjer) 398 

117.  Ventral  and  dorsal  zones  of  the  spinal  cord.     (Gordinier  and 

Qiiain  after  Kolliker) 399 

118.  Median  section  of  embryonic  brain  of  the  third  month.     (Mc- 

Murrich after  His) 406 

119.  Transverse  section  through  the  fore-brain  of  a  four  and  one 

half  weeks'  embryo.    (Gordinier  and  Quain  after  His)  407 

120.  Diagrammatic  sagittal  section  of  vertebrate  brain.     (Morrises 

Anatomy  after  Huxley) 409 

121.  Medial  sagittal  section  through  the  brain  of  an  embryo  of 

three  months  showing  the  primitive  fissures  on  the 
medial  surface  of  the  cerebral  hemisphere.  (McMur- 
rich after  Mihalkovicz) 411 

122.  The   fossa   cerebri    lateralis,  in   embryonic  brain  of   fourth 

month.  (After  McMurrich' s  Development  of  the  Human 
Body) 4^3 

123.  Permanent  fissures  and  sulci  on  the  convex  surface  of  the 

cerebrum  as  seen  in  a  seven  months'  embryo.  (Mc- 
Murrich after  Cunningham) 4^4 

124.  Dorsal  view  of  an  embroynic  brain,  the  roof  of  the  lateral  ven- 

tricles having  been  cut  away.  Embryo  of  12.6  mm. 
(McMurrich  after  His) 416 

125.  Transverse  section  of  medulla  from  an  embryo  of  9.1  mm. 

{McMurrich  after  His) 4^2 


XXXIV  LIST    OF    ILLUSTRATIONS. 

FIG.  PAGE 

126.  Transverse  section  of  the  medulla  from  an  embryo  of  eight 

weeks.     (McMurrich  after  His) 423 

127.  Transverse  section  of  the  spinal  cord,  from  an  embryo  of  (A) 

four  and  one-half  weeks,  and  (B)  of  three  months. 
(McMurrich  after  His) 427 

128.  Mode  of  origin  of  anterior  and  posterior  roots  of  spinal 

nerves.     Diagrammatic.     {Brubaker  and  Edinger  after 
His) 428 


ERRATA, 


Page  30.  Paragraph  two,  last  line,  last  word  should  be  brain- 
vesicles. 

Pag6  57.  Fig.  23.  "Intraparietal  sulcus,"  and  wherever  found 
should  be  written  Interparietal  sulcus. 

Page  108.  Paragraph  four,  fourth  line,  second  word  is  sulcus, 
instead  of  "fissure." 

Page  184.  Paragraph  one,  last  line  and  first  word  is  Alfred, 
instead  of  "Arthur." 

Page  264.  Fourth  line,  the  phrase  "anterior  ascending  cerebello- 
spinal tract,"  and  wherever  it  occurs,  should  read  Ascending  an- 
terior cerebello-spinal  tract. 

Page  265.  Paragraph  two,  third  line,  the  phrase  "anterior  de- 
scending cerebello-spinal  tract,"  should  stand  Descending  anterior 
cerebello-spinal  tract :  likewise,  wherever  the  quoted  phrase  is 
found. 

Page  277.     Third  Hne,  last  word  is  (Horsley). 

Page  286.  Paragraph  three,  last  sentence,  the  phrase  "fasciculus 
cerebello-spinalis,"  and  wherever  else  it  occurs  should  stand  thus — 
fasciculus  cerebello-spinalis  (posterior). 

Page  288.  Paragraph  three,  fifth  hne,  the  substantive  "cerebello- 
spinal fasciculus"  should  have  "posterior"  prefixed  so  as  to  read 
posterior  cerebello-spinal  fasciculus.  This  is  a  necessary  varia- 
tion from  the  BNA  and  applies  wherever  the  phrase  is  found. 

Page  291.  Last  Hne,  there  should  be  added  a  fifth  item,  viz.,  (e) 
the  medullary  striae. 


ERRATA.  XXXV 

Page  319.  Fifth  line,  common  sensory  should  be  added  under 
intermediate  nerve. 

Pag6  351.  Paragraph  three,  third  item,  (3)  should  be  omitted, 
as  no  posterior  root-fibers  decussate.  Intrinsic  fibers  only  cross 
through  the  gray  commissure   (Mott  and  Russell). 

Page  358.  To  the  last  sentence  should  be  added:  and  according 
to  Sir  Victor  Horsley  has  to  do  with  locomotion  (Brain,  1906). 

Page  410.  Fourth  line,  "callosal  fissure"  should  be  callosal 
sulcus. 


BRAIN  AND  SPINAL  CORD. 


CHAPTER  I. 

THE  MENINGES  OF  THE  BRAIN. 

(Meninges  Encephali.) 
Three  membranes  invest   the  brain   and   spinal   cord.     They 
are,  from   without  inward,  the  dura  mater,  the  arachnoid,  and 
the  pia  mater.     Each  membrane  forms  a  protecting  sheath  for 
the  cerebral  or  spinal  nerves  piercing  it. 

THE  DURA  MATER  OF  THE  BRAIN. 

(Dura  Mater  Encephali.) 

Structure  and  Relations. — It  is  a  very  dense  and  inelastic 
membrane  composed  of  white  fibrous  and  yellow  elastic  tissue 
lined  vdth  fiat  endothehal  cells,  which  constitute  its  internal 
surface.  In  children  it  is  closely  adherent  to  the  cranial  bones  of 
which  it  forms  the  real  periosteum;  but  it  is  attached  chiefly  at 
the  foramina  and  along  the  sutures  in  adults.  The  dura  of  the 
brain  is  made  up  of  two  layers  which  are  separable  up  to  the 
eighth  or  tenth  year.  The  external  layer  constitutes  the  endos- 
teum  of  the  cranial  bones.  It  is  their  nutrient  membrane. 
Through  the  cranial  foramina  and  sutures  it  is  continuous  with 
the  external  periosteum.  In  the  adult  the  internal  layer  of  the 
dura  separates  from  the  outer  layer  only  over  the  apex  of  the 
petrous  bone,  to  form  Meckel's  space  for  the  semilunar  ganglion 
(Gasseri);  at  the  foramina,  to  form  sheaths  for  the  nerves;  and, 
along  the  sinuses,  to  form  their  internal  boundary  and  to  produce 
the  great  incomplete  partitions,  called  processes,  which  project 
centrally  into  the  great  fissures  of  the  brain. 

Processes.  {Processus  durcE  matris).—Fvora  the  inner  surface 
of  the  dura  the  great  processes  are  given  off.     The  falx  cerebri 

I 


2  THE    MENINGES    OF    THE    BRAIN. 

and  falx  cerebelli  hang  vertically  in  the  longitudinal  fissure  of 
the  cerebrum  and  the  posterior  notch  of  the  cerebellum;  and, 
into  the  transverse  fissure  of  the  cerebrum,  extends  horizontally  the 
tentorium  cerebelli.  The  falx  cerebri  (Figs,  i,  and  4)  is  attached 
in  front  to  the  crista  galli  and  behind  to  the  internal  occipital  pro- 
tuberance and  superior  surface  of  the  tentorium;  the  falx  cere- 
belli (Fig.  i)  continues  from  the  inferior  surface  of  the  tentorium, 
along  the  occipital  crest,  to  the  posterior  border  of  the  foramen 
magnum.  The  bony  attachment  of  the  tentorium  cerebelli 
(Fig.  2)  is  to  the  internal  protuberance  and  the  lateral  arms  of 
the  crucial  ridge  forward  to  the  petrous  bone;  and,  then,  it  is 
along  the  superior  border  of  the  petrous  bone  to  the  clinoid  proc- 
esses of  the  sphenoid.  Between  its  chnoid  attachments  there  is 
a  deep  bay,  the  incisura  tentorii,  which  transmits  the  midbrain. 
The  diaphragma  sellae  is  a  small  centrally  perforated  sheet  of 
dura  which  covers  the  hypophyseal  fossa. 

Sinuses.  {Sinus  dura  matrls). — ^Large  venous  passages  lined 
with  endothelial  cells,  and  called  sinuses,  are  situated  between 
the  layers  of  the  dura  (Figs,  i,  2,  3  and  4).  In  the  convex  and  in 
the  free  border  of  the  falx  cerebri  are,  respectively,  the  superior 
sagittal  sinus  {s.  sagit talis  superior)  and  the  inferior  sagittal 
sinus  {s.  sagittalis  inferior).  The  superior  (Fig.  i)  extends 
from  the  foramen  caecum  back  to  the  confluens  sinuum  (torcular 
Herophili,)  located  at  the  internal  occipital  protuberance.  Having 
run  through  the  posterior  two-thirds  of  the  concave  border  of 
the  falx  cerebri,  the  inferior  sagittal  sinus  joins  the  great  cerebral 
vein  at  the  margin  of  the  tentorium  and  forms  the  straight  sinus 
(s.  rectus).  The  latter  runs  through  the  middle  of  the  tentorium 
to  the  confluens  (Fig.  2).  The  occipital  sinus  (5.  occipitalis) 
traverses  the  falx  cerebelli  from  the  foramen  magnum  upward 
to  the  same  point.  In  the  confluens  sinuum  the  transverse 
sinuses  {s.  transversi)  rise  (Fig.  2).  Grooving  the  horizontal 
arms  of  the  crucial  ridge,  each  runs  outward  in  the  tentorium  to 
the  base  of  the  petrous  bone,  where  it  receives  the  superior  petrosal 
sinus;  it  then  turns  downward  through  the  sigmoid  fossa,  com- 
municates with  the  occipital  sinus  and  unites  with  the  inferior 
petrosal  sinus  in  the  jugular  foramen.     Situated  on  either  side 


THE  DURA  MATER  OF  THE  BRAIN.  3 

of  the  sella  Turcica  is  a  continuation  of  the  ophthalmic  vein, 
the  large  cavernous  sinus  (s.  cavernosus)  (Fig.  3),  which  receives 
at  the  sphenoidal  hssure  the  spheno-parietal  sinus  {s.  alee  parvcs), 
the  course  of  which  is  along  the  posterior  border  of  the  lesser 
wing  of  the  sphenoid  bone.     At  the  posterior  clinoid  process    the 


Fig.    I. — Sagittal  section  of  skull,  showing  falx  cerebri,  falx  cerebelli,  part  of 
tentorium  cerebelli  and  sinuses.     (After  Morris's  Anatomy.) 

a.  Falx  cerebri,  b.  Superior  sagittal  sinus,  c.  Inferior  sagittal  sinus,  d.  Great  cere- 
bral vein.  e.  Straight  sinus,  f.  Tentorium  cerebelli.  g.  Transverse  sinus,  h.  Superior 
petrosal  sinus,  i.  Falx  cerebelli.  j.  Seventh  and  eighth  nerves,  k.  Ninth,  tenth,  and 
eleventh  nerves.  1.  Twelfth  nerve,  m.  Second  cervical  nerve,  n.  Fourth  nerve,  o.  Third 
nerve,  p.  Second  nerve,  q.  Middle  meningeal  arten.'.  r.  Internal  carotid  artery,  s.  Ver- 
tebral artery,  t.  Fifth  nerve,  u.  Sixth  nerve,  v.  Inferior  petrosal  sinus,  w.  First  cervical 
nerve,    x.  Ligamentum  denticulatum. 

cavernous  sinus  di^•ides  into  the  superior  petrosal  sinus  (s.  pelro- 
sus  superior)  and  the  inferior  petrosal  sinus  {s.  petrosus  injerior). 
The  sinus  intercavernosus  anterior  and  sinus  iniercavernosus 
posterior  extend  across  the  hypophyseal  fossa,  and  join  the  two 
cavernous  sinuses  together,  and  these  four  communicating  sinuses 


THE    MENINGES    OF    THE    BRAIN. 


constitute  the  circular  sinus  {s.  circularis)  (Fig.  3).  From  the 
bifurcation  of  the  cavernous  sinus  at  the  apex  of  the  petrous  bone, 
the  petrosal  sinuses  run  outward  along  the  corresponding  superior 
and  inferior  borders  of  that  bone.     The  superior  petrosal  sinus 


Fig.  2. — Horizontal  section  of  skull,  showing  tentorium  cerebelli,  tentorial  notch 
and  sinuses.     (After  Morris's  Anatomy.) 

a.  Infundibulum.  b.  Internal  carotid  artery,  c.  Optic  tract,  d.  Third  nerve,  e.  Basis 
pedunculi.  f.  Cerebral  aqueduct  (Sylvii).  g.  Quadrigeminal  body.  h.  Falx  cerebri. 
i.  Tentorium  cerebelli.  j.  Straight  sinus,  k.  Crista  galli.  1.  Optic  nerve,  m.  Spheno- 
parietal sinus,  n.  Middle  cerebral  artery,  o.  Anterior  cerebral  artery,  p.  Posterior  com- 
municating artery,  q.  Cavernous  sinus,  r.  Superior  cerebellar  artery,  s.  Posterior  cerebral 
artery,  t.  Superior  petrosal  sinus,  u.  Free  border  of  tentorium  bounding  tentorial  notch. 
V.  Transverse  sinus,    w.  Superior  sagittal  sinus. 

(Figs.  I  and  2)  empties  into  the  transverse  sinus  at  the  base  of 
the  petrous  bone;  the  inferior  petrosal  sinus,  in  its  course  to  the 
jugular  foramen,  is  joined  to  its  fellow,  across  the  basilar  process 
of  the  occipital  bone,  by  the  basilar  plexus  {p.  hasilaris)  and,  in 


THE  DURA  MATER  OF  THE  BRAIN. 


5 


the  jugular  foramen,  unites  with  the  transverse  sinus  in  forming 
the  internal  jugular  vein. 
Arachnoid   Granulations    (Fig.  25). — ^.\long  and  within  the 


Fig.  3. — Sinuses  in  the  base  of  the  cranium,  also  meningeal  arteries. 
{Ahev  Morris's  Anatomy.) 

a.  Meningeal  branch  of  anterior  ethmoidal  artery,  b.  Meningeal  branch  of  posterior  eth- 
moidal artery,  c.  Middle  meningeal  artery,  d.  Ophthalmic  division  of  fifth  nerve,  e.  Third 
nerve,  f.  Cavernous  sinus,  g.  Fourth  nerve,  h.  Auditory  and  facial  nerves,  i.  Superior 
petrosal  sinus,  j.  Inferior  petrosal  sinus,  k.  Petro-squamosal  sinus.  1.  Accessory  nerve, 
m.  Sigmoid  part  of  transverse  sinus,  n.  Posterior  meningeal  branch  of  vertebral  artery. 
o.  Left  marginal  sinus,  p.  Left  transverse  sinus,  q.  Superior  sagittal  sinus,  r.  Circular 
sinus,  s.  Carotid  artery,  t.  Sixth  nerve,  u.  Basilar  artery,  v.  Basilar  ple.xus  of  veins. 
w.  Auditory  artery,  x.  Vertebral  artery,  y.  Glossopharyngeal  and  vagus  nerA-es.  z.  An- 
terior spinal  artery,  aa.  Hypoglossal  ner\'e.  bb.  Accessory  nerve,  cc.  Right  marginal 
sinus,     dd.  Occipital  sinus,    ee.  Right  transverse  sinus. 


superior  sagittal,  the  straight,  the  transverse,  the  petrosal  and 
the  cavernous  sinuses  are  the  granulationes  arachnoideales  (Pac- 
chionian bodies).     These  granulations   are   enlarged  vilh  of  the 


O  THE    MENINGES    OF    THE    BRAIN. 

arachnoid  (Fig.  4)  and  seem  to  afford  an  outlet  for  the  sub- 
arachnoid fluid  into  the  sinuses.  They  are  said  to  make  their 
appearance  about  the  tenth  year  and  to  be  more  numerous  and 
larger  in  the  male  sex.  Some  of  them  by  absorption  produce 
depressions  in  the  cranial  bones  called  joveola  granulares. 

The  arteries  which  supply  the  dura  are  (i)  The  anterior 
meningeal  irom  the  anterior  ethmoidal  branch  of  the  ophthalmic. 
(2)  The  middle  meningeals,  viz.,  the  great  and  the  small  middle 
meningeal   from   the   internal   maxillary,    the   meningeal  branch 


Fig.  4. — Coronal  section  showing  falx  cerebri,  superior  sagittal  sinus  and  arachnoid 
granulations.     {Gordinier  after  Key  and  Retzius.) 

a.  Subarachnoid  space,    b.  Superior  sagittal  sinus,    c.  Arachnoid  granulations  (Pacchioni). 
d.  Dura  mater,     e.  Falx  cerebri,    f.  Anterior  cerebral  artery,    g.  Corpus  callosum. 

of  the  lacrimal  and  of  the  internal  carotid,  and  the  meningeal 
branch  of  the  ascending  pharyngeal  which  enters  the  middle 
fossa  of  the  cranium  through  the  lacerate  foramen.  (3)  The 
posterior  meningeal  arteries,  which  rise  from  the  ascending 
pharyngeal,  the  occipital  and  the  vertebral  and  are  distributed 
to  the  dura  over  the  posterior  cranial  fossa. 

The  great  middle  meningeal  artery  (arteria  meningea  media) 
is  much  the  largest  and  is  most  important  (Fig.  5).  It  overlies 
the  motor  and  somgesthetic  areas  of  the  brain.  Like  the  other 
meningeal  arteries  it  is  usually  accompanied  by  two  veins.     Ascend- 


THE  DURA  MATER  OE  THE  BRAIN.  7 

ing  from  the  foramen  spinosum  it  divides  near  the  upper  border 
of  the  squamosa  into  two  large  branches,  the  anterior  and  posterior. 
The  posterior  runs  horizontally  backward  just  below  the  squamo- 
parietal  suture  and  then  ascends  over  the  posterior  half  of  the 
parietal  bone.  The  anterior  branch  runs  upward  a  half-inch 
behind  the  coronal  suture.  It  may  be  located,  according  to 
Quain,  at  one  inch,  at  one  inch  and  a  half,  and  at  two  inches 


Fig.  5. — Median  section  of  skull  showing  middle  meningeal  artery. 
(After  Morris's  Anatomy.) 


behind  the  zygomatic  process  of  the  frontal  bone  and  above  the 
zygomatic  process  of  the  temporal  bone. 

The  following  nerves  give  branches  to  the  dura: — Troch- 
lear, ophthalmic,  semilunar  ganglion,  vagus  and  hypoglossal 
of  the  cerebral  group;  and  the  sympathetic.  The  motor  fibers 
supply  the  meningeal  arteries. 

Six  Points  of  Difference  in  the  Dura  of  the  Cord. — ^.\bsencc  of 
processes,  of  sinuses,  of  arachnoid  granulations,  and  of  periosteal 


8  THE    MENINGES    OF    THE    BRAIN. 

function.  It  is  covered  on  both  surfaces  by  endothelium  and 
is  separated  from  the  vertebras  by  areolar  tissue,  fat  and  the  plexus 
of  internal  vertebral  veins. 

THE  ARACHNOID  OF  THE  BRAIN. 

(Arachnoidea  Encephali.) 

In  structure  it  is  a  delicate,  fibrous,  web-like  membrane  covered 
externally  with  endothelium.  Internally  it  is  joined  to  the  pia 
mater  by  innumerable  fibrous  trabeculse,  the  subarachnoid  tissue 
(Fig.  4).  The  trabeculse  are  ensheathed  and  all  subarachnoid 
spaces  hned  with  a  single  layer  of  endothelial  cells,  hence  both 
surfaces  are  formed  of  endothelium.  Conical  elevations  of 
fibrous  tissue  with  their  investing  endothelium  constitute  the 
villi  seen  on  the  outer  surface.* 

Relations.— The  arachnoid  follows  the  inner  surface  of  the 
dura  and  is  prolonged,  as  a  sheath,  upon  the  nerves  which  pierce 
it.  It  does  not  dip  into  the  sulci  of  the  cerebrum  (Fig.  6) ;  but 
only  into  the  lateral  fissure  and  the  longitudinal  fissure,  and  does 
not  reach  to  the  bottom  of  the  latter.  From  the  pia  it  is  sepa- 
rated by  the  subarachnoid  spaces  (cava  suharachnoidealia).  The 
anterior  subarachnoid  space  (Fig.  6)  includes  the  cistema  pontis, 
cisterna  interpeduncularis,  cisterna  chiasmatis  and  cisterna 
fossae  laterahs  cerebri.  It  is  located  in  front  of  the  medulla,  pons 
and  mid-brain  and  between  the  temporal  lobes  of  the  cerebrum. 
The  posterior  subarachnoid  space  (Fig.  6)  is  located  behind  the 
medulla  and  cerebellum.  It  embraces  the  cisterna  cerebello- 
meduUaris,  a  space  between  the  medulla  and  cerebellum,  and  the 
cistema  venae  cerebri  magnae,  situated  along  the  straight  sinus 
and  the  great  cerebral  vein.  These  two,  the  anterior  and  posterior, 
are  the  largest  subarachnoid  spaces  and  they  contain  much  of 
the  subarachnoid  fluid.  But  in  the  cerebral  sulci  and  fissures 
there  are  streams  of  this  fluid  which  constitute  the  subarachnoid 
rivulets.     The    anterior    subarachnoid    space    has    slit-like   co?n- 

*  Some  authors  consider  this  membrane,  as  just  described  above, 
merely  as  a  visceral  layer  of  the  arachnoid,  and  regard  the  endothelial 
lining  of  the  dura  mater  as  its  parietal  layer.  According  to  such, 
therefore,  the  subdural  space  becomes  the  arachnoid  space. 


THE    PIA    MATER    OF    THE    BRAIN.  9 

munications  with  the  inferior  horn  of  the  lateral  ventricle;  the 
posterior  space  communicates  with  the  fourth  ventricle  (Fig.  8) 
through  the  median  aperture  {apertura  mediana  ventriculi  guarii, 
Magendi)  and  the  lateral  apertures  (apertures  laterales  ventriculi 
quarii,  Key  and  Retzii). 

The  vessels  seen  for  a  short  distance  in  the  arachnoid  belong 
to  the  pia  mater.  Its  nerves  are  doubtful.  Perhaps  branches 
of  the  mandibular,  of  the  facial  and  of  the  accessory  supply  it. 

Pia  mater        Subarachnoid  space 


-  Arachnoid 


Third^ventricle 
Infundibulum 


Cisterna  mterpedunculans 
Cisterna  pontis 


Fourth 
ventricle 
Cisterna  cere- 
bello-medul- 

laris 
Median  apert- 
ure (Magendi) 


Fig.  6. — Diagram  of  pia  and  arachnoid,  showing  subarachnoid  spaces. 
(After  Morris's  Anatomy.) 


In  the  arachnoid  of  the  cord  few^er  trabeculse  join  it  to  the  pia; 
and  these,  in  great  part,  are  collected  to  form  a  fenestrated  sep- 
tum in  the  posterior  median  line  (Fig.  97,  A).  The  external 
spinal  veins  are  covered  by  the  spinal  arachnoid,  they  lie  between 
it  and  the  pia. 

THE  PIA  MATER  OF  THE  BRAIN. 

(Pia  Mater  Encephali.) 

Structure  and  Relations. — It  is  a  vascular  membrane  com- 
posed of  a  close  network  of  veins  and  arteries  held  together  by 


lO  THE    MENINGES    OF    THE    BRAIN. 

fib ro- elastic  areolar  tissue  (Fig.  9).  The  endothelium  covering  its 
outer  surface  is  continuous  with  that  ensheathing  the  subarachnoid 
trabeculae.  The  pia  closely  follows  the  brain  surface  (Fig.  6). 
Internally,  it  sends  supporting  trabeculae  into  the  brain,  which 
transmit  blood-vessels;  and  externally  it  forms  an  investing 
sheath  for  each  cerebral  nerve. 

Folds. — ^Two  important  processes  are  formed  by  the  pia  mater: 
(i)  The  chorioid  tela  of  the  third  ventricle  {tela  chorioidea 
ventriculi  tertii)  is  pushed  forward  into  the  anterior  part  of  the 
transverse  fissure  of  the  cerebrum  between  the  fornix  and  the 
interbrain  (Fig.  6).  Hence  the  old  name,  velum  interpositum.  It 
is  triangular  in  shape,  with  apex  directed  forward  (Fig.  7).  Each 
lateral  border  is  tucked  into  the  chorioidal  fissure  of  the  cerebral 
hemisphere  and  enters  into  the  floor  of  the  lateral  ventricle,  while 
the  median  part  of  the  fold  is  in  the  roof  of  the  third  ventricle. 
Between  the  two  layers  of  this'  chorioid  tela  is  some  areolar  tissue 
through  which  run  backward  the  two  internal  cerebral  veins  and 
unite  near  the  base  of  the  tela  to  form  the  great  cerebral  vein. 
The  chorioid  plexuses  of  the  lateral  and  the  third  ventricles  oc- 
cupy, respectively,  the  lateral  borders  and  the  median  area  of  this 
chorioid  tela.  (^2)  A  second  fold  of  pia  mater  is  tucked  into 
the  transverse  fissure  of  the  cerebellum,  dorsal  to  the  medulla 
oblongata  and  ventral  to  the  posterior  median  part  of  the  cere- 
bellum (Fig.  6).  It  is  called  the  chorioid  tela  of  the  fourth 
ventricle  {tela  chorioidea  ventriculi  quarti)  because  its  inferior 
layer  enters  into  the  roof  and  contains  the  chorioid  plexus  of  that 
ventricle.  This  lower  layer  invests  the  posterior  surface  of  the 
medulla  and  the  roof-epithelium  of  the  fourth  ventricle  (Fig.  8). 
It  is  pierced  by  three  foramina  which  are  situated  as  follows: 
One  over  each  lateral  angle  of  the  fourth  ventricle,  the  lateral 
apertures  (Key  and  Retzii),  and  one  over  its  inferior  angle.  The 
latter  is  the  largest  and  is  called  the  median  aperture  {Magendi). 
Those  three  foramina  establish  communication  between  the  pos- 
terior subarachnoid  space  and  the  fourth  ventricle. 

The  arteries  of  the  pia  mater  supply  the  brain  (Figs.  9,  10, 
II  and  12).  They  are  the  anterior,  middle  and  posterior  cerebrals; 
the  anterior  and  posterior  chorioidals;  and  the  anterior  and  pos- 


THE    PIA    MATER    OF    THE    BRAIN. 


II 


Fig.   7. — Horizontal  section  of  cerebrum.     Fornix  turned  back,  showing  chorioid 
tela  of  third  ventricle,  and  internal  cerebral  veins.     (Original.) 


THE    PIA    MATER    OF    THE    BRAIN. 


13 


tenor  inferior  cerebellar  and  the  superior  cerebellar  with  many 
branches. 

The  veins  are  more  numerous  than  the  arteries  in  the  pia: 
the  internal  and  great  cerebral  veins,  the  veins  of  the  chorioid 
plexuses  of  the  lateral,  third  and  fourth  ventricles  and  the  basilar 
vein;  the  cerebral  veins,  superior,  medial  and  inferior;  and  the 
superior  and  inferior  cerebellar  veins.  All  of  them  empty  into 
the  sinuses  (see  page  2). 


Inferior  quadrigeminal 

colliculus 

Fourth  nerve 


Superior  medullary 
velum 


Restiform  body 

Tffinia 

Epithelial  roof  of 

fourth  ventricle 

Cuneate  tubercle' 

Clava- 

Tuberculum  cinereurr 


Frenulum  veli 
Laterali  fillet 


Inferior  medullary 
velum 
Chorioid  plexus 

Median  aperture 
(Magendi) 

Obex 


Fig.  8. — Roof  and  lateral  walls  of  fourth  ventricle,  and  its  chorioid  plexuses. 
(After  Morris's  Anatomy.) 


Seven  cerebral  nerves— 3d,  5th,  6th,  7th,  9th,  loth  and  nth— 
and  the  sympathetic  supply  the  pia  mater  and  its  blood-vessels. 

The  pia  mater  of  the  spinal  cord  has  two  layers,  the  outer  of 
which  is  the  more  vascular  and  contains  the  spinal  arteries  and 
the  tributaries  of  the  external  spinal  veins.  It  forms  three  proc- 
esses, namely,  the  anterior  septum,  which  occupies  the  anterior 
median  fissure,  and  the  ligamentum  denticulatum  of  each  side. 


14  THE    MENINGES    OF    THE    BRAIN. 

THE  BLOOD  SUPPLY  OF  THE  BRAIN. 

The  brain  is  furnished  with  blood  by  the  internal  carotid  and 
vertebral  arteries  (Fig.  9).  The  internal  carotid  artery  (a. 
carotis  interna)  gives  origin  to  the  anterior  and  the  middle  cere- 
bral, the  anterior  chorioidal  and  the  posterior  communicating; 
the  vertebral  artery  {a.  vertebralis)  gives  off  the  anterior  and 
posterior  spinal  and  the  posterior  inferior  cerebellar  and  then 
unites  with  its  fellow  at  the  inferior  border  of  the  pons  and  forms 
the  basilar  artery.  The  basilar  artery  {a.  hasilaris)  runs  upward 
the  length  of  the  pons  and  terminates  in  the  two  posterior  cerebral 
arteries  and,  furthermore,  gives  off  the  following  collateral  branches, 
viz.,  the  anterior  inferior  cerebellar,  the  pontal,  the  internal  audi- 
tory and  the  superior  cerebellar.  Certain  of  these  arteries  form 
a  wonderful  circular  anastomosis  at  the  base  of  the  brain,  called 
the  arterial  circle  and  the  distribution  of  that  circle  is  to  the  cere- 
brum (Figs.  9  and  10);  while  the  rhombencephalon  (pons,  cere- 
bellum and  medulla)  is  supplied  by  the  remainder  of  the  arteries 
above  enumerated.  It  is  therefore  convenient  to  describe  the 
circulation  of  the  brain  under  two  heads:  (A)  The  circulation 
of  the  cerebrum,  and  (B)  The  circulation  of  the  rhomben- 
cephalon. 

A.     THE  CEREBRAL  CIRCULATION,  ARTERIES. 

The  Arterial  Circle.  {Circulus  arteriosis,  Willisi). — ^The  arter- 
ies which  supply  the  cerebrum  freely  communicate  in  the  arterial 
circle,  which  is  really  a  heptagon  extending  from  a  point  in  the 
longitudinal  fissure  anterior  to  the  optic  chiasma,  back  to  the  pons 
(Fig.  9).  It  is  about  an  inch  and  a  half  long,  and  from  a  half 
to  one  inch  in  transverse  diameter.  In  front  are  the  anterior 
cerebral  arteries  converging  forward  from  the  internal  carotids 
and,  through  the  anterior  communicating  artery  {a.  communicans 
anterior),  uniting  just  as  they  enter  the  longitudinal  fissure  of  the 
cerebrum.  These  vessels  form  three  sides  of  the  heptagon  and 
the  front  of  the  circle.  On  either  side,  the  posterior  communic- 
ating artery  {a.  communicans  posterior)  which  connects  the  internal 
carotid  with  the  posterior  cerebral  artery,  forms  the  lateral  bound- 


THE    CEREBRAL    CIRCULATION,    ARTERIES. 


15 


ary  of  the  circle.  The  posterior  cerebral  arteries  bound  the 
circle  behind,  and  so  complete  it  (Fig.  10).  The  large  distal 
branches  of  the  arteries  which  are  connected  with  the  arterial 
circle  are  distributed  chiefly  to  the  cortex  and  medulla  of  the 
hemispheres;    while    the    small  proximal  branches  supply   the 


Fig.  g. — Arterial  circle  and  its  branches  on  the  base  of  the  brain. 
(After  Morris's  Anatomy.) 

a.  Anterior  cerebral  artery,  b.  Middle  cerebral  artery,  c.  Internal  carotid  artery,  d.  Pos- 
tero-median  ganglionic,  e.  Posterior  cerebral  artery,  f.  Superior  cerebellar  artery,  g.  An- 
terior inferior  cerebellar  artery,  h.  Vertebral  artery,  i.  Posterior  inferior  cerebellar  artery. 
j.  Anterior  communicating  artery,  k.  Antero-lateral  ganglionic.  I.  Anterior  chorioid. 
m.  Posterior  communicating  artery,  n.  Posterior  chorioid.  o.  Basilar  artery,  p.  Hemis- 
phere of  cerebellum  cut  away.    q.  Anterior  spinal  artery. 


ganglia  and  the  inter-brain.     The  former  belong  to  the  cortical 
system  (i^i),  the  latter  to  the  gangHonic  system  (A2). 

Al.  The  Cortical  System  of  Arteries. — The  cortical  arterial 
system  comprises  the  distal  portions  of  the  anterior,  middle  and 
posterior  cerebral  and  the  chorioidal  arteries.     The  branches  of 


1 6  THE    MENINGES    OF    THE    BRAIN. 

these  great  vessels  pierce  the  hemispheres  perpendicularly  to  the 
surface.  They  are  distributed,  the  short,  to  the  cortex,  and  the 
long,  to  the  medulla  of  the  hemispheres.  To  a  limited  extent 
they  anastomose  with  one  another,  but  they  do  not  communicate 
with  the  ganghonic  system. 

The  anterior  cerebral  artery  {a.  cerebri  anterior,  Figs.  9  and 
12),  a  branch  of  the  internal  carotid,  runs  forward  and  toward 
the  median  hne  above  the  optic  nerve  and  enters  the  longitudinal 
fissure;  it  is  here  joined  to  its  mate  by  a  very  short  artery,  the 
anterior  communicating.  Winding  around  the  genu  of  the  corpus 
callosum,  it  runs  back  on  the  medial  surface  of  the  hemisphere  to 
the  occipito-parietal  sulcus.  It  gives  origin  to  the  antero-median 
ganghonic  arteries,  and  to  four  groups  of  cortical  branches: 
(i)  The  internal  orbital  artery  (Figs.  9  and  .10)  which  supplies 
the  medial  orbital  gyrus,  the  gyrus  rectus,  the  optic  chiasma  and 
the  olfactory  bulb,  tract,  medial  and  intermediate  striae,  triangle, 
and  parolfactory  area.  (2)  The  anterior  internal  frontal  (Fig.  12) 
which  enters  the  anterior  parts  of  the  gyrus  cinguli  and  superior 
frontal  gyrus  on  the  medial  surface  and  of  the  superior  and  middle 
frontal  gyri  on  the  convex  surface.  (3)  The  middle  internal  frontal 
branches,  which  are  distributed  to  the  middle  part  of  the  gyrus 
cinguli,  to  the  paracentral  lobule  and  to  the  upper  portions  of  the 
superior  frontal  and  the  anterior  and  posterior  central  gyri.  (4) 
The  posterior  internal  frontal  branches,  which  run  back  to  the 
occipito-parietal  sulcus.  They  supply  nearly  the  whole  corpus 
callosum,  the  posterior  half  of  the  gyrus  cinguli,  a  part  of  the 
paracentral  lobule,  the  praecuneus,  and  the  superior  parietal 
lobule. 

The  middle  cerebral  artery  (a.  cerebri  media,  Figs.  10  and  11) 
crosses  the  anterior  perforated  spot  and  runs  in  the  lateral  fissure 
of  the  cerebrum  to  the  posterior  sulcus  circularis  (Reili)  where 
it  breaks  up  into  several  parieto-temporal  branches.  It  gives 
origin  to  the  antero-lateral  ganglionic  arteries,  and  to  four  cortical 
branches:  (i)  The  lateral  orbital  branches  are  distributed  to 
the  anterior  and  posterior  orbital  and  the  inferior  frontal  gyri. 
(2)  The  ascending  frontal,  two  branches,  which  follow  the  pre- 
central  and  central  sulci,  supply  the  anterior  central  gyrus  and 


THE    CEREBRAL    CIRCULATION,    ARTERIES.  1 7 

the  posterior  fourth  of  the  middle  frontal  gyrus.  (3)  The  ascend- 
ing parietal,  whose  course  is  along  the  interparietal  sulcus,  fur- 
nishes blood  to  the  posterior  central  gyrus  and  the  adjacent 
parts  of  the  superior  and  inferior  parietal  lobules.  (4)  The 
parieto-temporal  arlcries,  which  comprise  two  polar  branches 
to  the  temporal  lobe  and  a  large  posterior  branch.  The  latter 
runs  in  the  posterior  ramus  of  the  lateral  cerebral  fissure  to  its 
upturned  posterior  end  and  there  bifurcates  into  a  parietal  and  a 
temporal  branch,  which  just  pass  the  anterior  Umit  of  the  occip- 
ital lobe.  The  entire  distribution  of  the  parieto-temporal  arteries 
is  to  the  temporal  pole  and  to  the  superior,  middle  and  part  of 
the  inferior  temporal  gyri;  to  the  major  parts  of  the  supramar- 
ginal,  angular  and  post-parietal  gyri,  and  to  a  very  small  portion 
of  the  superior  and  lateral  occipital  gyri. 

The  posterior  cerebral  artery  (a.  cerebri  posterior),  a  ter- 
minal branch  of  the  basilar,  lies  in  the  posterior  boundary  of  the 
arterial  circle  and  is  joined  to  the  internal  carotid  by  the  posterior 
communicating  artery  (Figs.  10  and  12).  It  winds  backward 
between  the  midbrain  and  gyrus  hippocampi  to  the  tentorial 
surface  of  the  cerebral  hemisphere  where,  just  beyond  the  splenium 
of  the  corpus  callosum,  it  terminates  in  the  calcarine  and  occipito- 
parietal branches.  From  the  posterior  cerebral  arteries  originate 
the  postero-median  and  the  postero-lateral  ganghonic,  and  two 
or  more  posterior  chorioidal  arteries  and  three  cortical 
branches:  (i)  The  temporal  branches,  often  an  anterior,  middle 
and  posterior  temporal,  which  supply  the  hippocampal  and  the 
fusiform  gyri  and  a  part  of  the  lingual  and  of  the  inferior  tem- 
poral gyrus. 

(2)  The  calcarine  artery,  which  runs  along  the  iissure  of  the 
same  name  and  suppHes  the  cuneate  and  lingual  gyri;  also  the 
pole  and  the  lateral  and  superior  gyri  of  the  occipital  lobe.  (3) 
The  occipito- parietal  artery,  a  single  branch,  which  runs  along 
the  sulcus  occipito-parietahs  over  the  supero-medial  border  to 
the  convex  surface  of  the  cerebral  hemisphere  and  is  distributed 
to  the  cuneus,  the  pr^ecuneus  and  the  superior  occipital  gyrus. 

The  posterior  chorioidal  arteries  {artericr  chorioidea  poste- 
rior es,  Figs.  7,  9  and  10)  two  or  more  in  number  are  branches  of 


l8  THE    MENINGES    OF    THE    BRAIN. 

the  posterior  cerebral  which  run  forward  in  the  transverse  and 
chorioidal  fissures  of  the  cerebrum  to  the  chorioid  plexuses  of  the 
lateral  and  third  ventricles  (Fig.  7). 

The  anterior  chorioidal  arteries  (a.  chorioidea  anterior)  rises 
from  the  internal  carotid  artery  just  proximal  to  its  anterior  and 
middle  cerebral  branches,  and  runs  backward  and  outward  along 
the  optic  tract  to  the  anterior  inferior  end  of  the  chorioidal  fissure, 
which  it  enters  (Fig.  10).  It  terminates  in  the  chorioid  plexus 
of  the  inferior  horn  of  the  lateral  ventricle,  and  gives  collateral 
branches  to  the  optic  tract,  the  gyrus  hippocampi,  the  fascia 
dentata,  the  hippocampus,  the  crus  of  the  fornix  and  the  posterior 
part  of  the  internal  capsule. 

A2.  The  Ganglionic  System  of  Arteries. — Small  arteries 
from  the  arterial  circle  and  from  the  cerebral  arteries  near  the 
circle  constitute  this  system  (Fig.  10).  The  arteries  pass  to 
their  distribution  without  communicating  with  one  another  or 
with  the  cortical  arteries.  They  are  the  end-arteries  of  Cohnheim. 
Between  the  cortical  and  ganglionic  systems,  there  is  an  area 
poorly  supplied  with  blood.  That  is  the  area  of  cerebral  softening 
in  old  age.  The  ganglionic  system  of  arteries  is  made  up  of  six 
groups  of  small  vessels:  The  antero-median,  the  right  and  left 
antero-lateral,  the  postero-median  and  the  right  and  left  postero- 
lateral. 

The  antero-median  ganglionic  arteries  rise  from  the  anterior 
cerebrals  in  front  of  the  optic  chiasma  (Fig.  10).  They  supply 
the  chiasma,  the  lamina  terminalis,  the  rostrum  of  the  corpus 
callosum,  the  septum  pellucidum  and  the  head  of  the  caudate 
nucleus. 

The  antero-lateral  ganglionic  arteries  take  their  origin,  on 
either  side,  from  the  middle  cerebral  artery,  a  little  outside  the 
arterial  circle  (Fig.  10).  They  pierce  the  anterior  perforated 
substance  and  are  distributed  to  the  striated  body,  internal  capsule 
and  thalamus.  The  largest  one  of  this  group  is  the  lenticulo- 
striate  artery.  It  supplies  the  greater  part  of  the  corpus  striatum. 
On  account  of  its  frequent  rupture,  it  is  called  the  artery  of  cerebral 
hemorrhage  (Charcot). 

Postero-median   Ganglionic  Arteries. — ^These   are  branches 


THE    CEREBRAL    CIRCULATION,    ARTERIES.  IQ 


Fig.  lo. — Arterial  circle  and  its  branches  on  the  base  of  the  cerebrum. 
{Gordinier  after  Duret.) 

On  the  left  side  of  the  brain  the  temporal  lobe  is  cut  away  so  as  to  open  the  inferior  and 
posterior  horns  of  the  lateral  ventricle.  The  mid-brain  is  divided  close  above  the  pons  and 
the  posterior  cerebral  arteries  are  cut  at  their  origin  from  the  basilar. 

Ganglionic  arteries:  am.  Antero-median  group  arising  from  the  anterior  cerebral,  al.  An- 
tero-lateral  group,  from  the  middle  cerebral,  pm,  pi  {on  the  optic  thalamus).  Postero- 
median and  postero-lateral  groups,  from  the  posterior  cerebral. 

Chorioidal  arteries:  a  ch.  Anterior,  from  the  internal  carotid,  p  ch  (on  the  splenium).  Pos- 
terior, from  the  posterior  cerebral. 

Cortical  arteries:  i,  i.  Inferior  internal  frontal,  from  the  anterior  cerebral.  2.  Inferior  ex- 
ternal frontal.  3.  Ascending  frontal.  4.  Ascending  parietal,  and  5,  temporo-parietal  from 
the  middle  cerebral.  6.  Anterior  temporal,  7,  posterior  temporal,  and  8,  occipital,  from  the 
posterior  cerebral. 


VEINS    OF   THE    CEREBRUM.  21 

of  the  posterior  cerebral  and  posterior  communicating  arteries 
(Figs.  9  and  lo).  They  supply  the  interpeduncular  structures, 
the  peduncles  and,  after  piercing  the  posterior  perforated  sub- 
stance, the  walls  of  the  third  ventricle  and  the  medial  parts  of 
the  thalami. 

Postero-lateral  Ganglionic  Arteries. — ^They  rise,  on  either 
side,  from  the  posterior  cerebral  artery  after  it  has  wound  around 
the  base  of  the  peduncle  (Fig.  lo).  They  are  distributed  to  the 
posterior  part  of  the  thalamus;  the  geniculate,  quadrigeminal  and 
pineal  bodies;  the  quadrigeminal  brachia  and  the  pedunculus 
cerebri.  The  superior  cerebellar  arteries  send  several  branches 
to  the  dorsum  of  the  mid-brain,  and  complete  the  arterial  supply 
of  the  cerebrum. 

VEINS  OF  THE  CEREBRUM. 

The  Internal  Veins  of  the  Cerebrum. — ^The  veins  of  the  cere- 
brum {vencB  cerebri)  are  classed  as  internal  and  external.  The 
trunks  of  the  internal  veins  are  located  largely  in  the  chorioid 
tela  of  the  third  ventricle,  near  the  apex  of  which  the  internal 
cerebral  vein  is  formed:  while  at  the  base  of  this  chorioid  tela 
the  internal  cerebral  vein  unites  with  its  mate  in  forming  the 
great  cerebral  vein. 

The  internal  cerebral  vein  (v.  cerebri  interna)  is  formed  by 
the  union  of  the  chorioidal,  the  terminal  and  the  vein  of  the  sep- 
tum pellucidum.  It  runs  backward  between  the  layers  of  the 
chorioid  tela  of  the  third  ventricle  (Fig.  7),  receiving  several 
small  collaterals  from  the  tela,  from  the  pineal  and  quadrigeminal 
bodies  and  the  corpus  callosum;  and,  finally,  it  receives  the  basilar 
vein  from  the  inferior  surface  of  the  cerebral  hemisphere.  Under 
the  splenium  of  the  corpus  callosum  it  joins  the  internal  cerebral 
vein  of  the  opposite  side  and  forms  the  great  cerebral  vein. 

The  great  cerebral  vein  (v.  cerebri  magna,  Galeni)  is  a  short, 
thick,  median  trunk,  a  half-inch  long  (Fig.  i).  At  the  posterior 
border  of  the  tentorial  notch  it  is  joined  by  the  inferior  sagittal 
sinus  and  then  continued  as  the  sinus  rectus.  This  short  vein 
receives  collateral  tributaries  from  the  sryrus  cinguli,  from  the 


22 


THE    MENINGES    OF    THE    BRAIN. 


medial  and  tentorial  surfaces  of  the  occipital  lobe  and  from  the 
superior  surface  of  the  cerebellum  (Cunningham). 

Small  nameless  internal  veins  issue  from  all  parts  of  the  exterior 
surface  of  the  cerebrum  and  form  the  external  veins. 

The  External  Veins  of  the  Cerebrum. — ^The  external  cerebral 
veins  {vena  cerebri  externce)  are  numerous  and  of  large  size.  They 
ramify  in  the  pia  mater  and  in  the  subarachnoid  space.  They 
empty  into  the  dural  sinuses,  as  a  rule,  against  the  current  in  the 
sinuses,  and    they   form    two    principal    groups:     The   superior 


Fig.  1 1 . — Middle  cerebral  artery  and  branches.  {Gordinier  after  Quain  and  Charcot.) 

CENT.     Antero-lateral  group  of  ganglionic  arteries,     i.    Inferior  external  frontal  artery. 
2.  Ascending  frontal  artery.    3.  Ascending  parietal  artery.    4.  Parieto-temporal  artery. 


cerebral  and  the  inferior  cerebral,  and  a  very  small  group,  on 
the   medial    cerebral  surface,  called  the  medial  cerebral  veins. 

The  superior  cerebral  veins  {vencB  cerebri  superiores),  twelve 
or  more  in  number,  carry  away  the  blood  from  the  superior  surface 
of  the  hemisphere.  They  run  obliquely  upward  and  forward 
into  the  superior  sagittal  sinus.  Just  before  emptying  into  the 
sinus  they  receive  most  of  the  medial  veins. 

The  Medial  Cerebral  Veins.  {Vence  cerebri  mediales). — ^They 
drain  the  marginal  part  of  the  medial  surface  of  the  hemisphere. 


VEINS    OF    THE    CEREBRUM.  27, 

The  veins  of  this  group  which  do  not  emi)ty  into  the  superior 
cerebral  veins  unite  and  form  the  inferior  sagittal  sinus,  and  the 
anterior  cerebral  vein  which  drains  much  of  the  medial  surface. 

The  inferior  cerebral  veins  {vence  cerebri  injeriores)  drain  the 
base  of  the  cerebrum  and  the  lower  border  of  its  convex  sur- 
face. On  the  tentorial  surface  of  the  hemisphere,  from  three  to 
five  of  these  veins  empty  into  the  transverse  and  superior  petrosal 
sinuses.  Those  from  the  temporal  and  frontal  lobes  empty  into 
the  spheno-parietal  sinus  and  cavernous  sinus,  excepting  the 
small  anterior  cerebral  vein  and  the  deep  middle  cerebral  vein, 
which  unite  with  the  inferior  striate  veins  in  forming  the  basilar 
vein.  The  anterior  cerebral  vein  accompanies  the  artery  of  the 
same  name.  It  drains  the  gyrus  cinguli  and  corpus  callosum, 
chiefly;  and,  in  the  fossa  lateralis  cerebri,  unites  with  vessels  that 
descend  from  the  corpus  striatum,  the  inferior  striate  veins,  and 
with  the  deep  middle  cerebral  vein.  The  deep  vena  cerebri  media 
drains  the  insula  and  the  opercula,  in  part,  and  deep  in  the  fissure 
runs  medianward  to  the  fossa  lateralis  cerebri  and  helps  to  form 
the  basilar.  The  basilar  vein  {v.  basilaris),  is  formed  at  the 
anterior  perforated  spot  by  the  deep  middle  cerebral,  the  inferior 
striate  and  the  anterior  cerebral  veins.  Running  backward  it 
receives  additional  blood  from  the  interpeduncular  structures, 
the  hippocampal  gyrus  and  the  inferior  horn  of  the  lateral  ventricle, 
and  from  the  mid-brain,  as  it  winds  around  it  to  empty  into  the 
corresponding  internal  cerebral  vein  near  its  termination.  In  the 
fissura  lateralis  cerebri  (Sylvii)  runs  also  a  superficial  vein,  called 
the  superficial  middle  cerebral  (v.  cerebri  media)  which  receives 
tributaries  from  the  surfaces  adjacent  to  the  posterior  ramus  and 
the  stem  of  that  fissure  and  empties  into  the  cavernous  sinus;  but 
it  may  have  two  other  outlets,  viz.,  the  transverse  sinus  and  the 
superior  sagittal  sinus.  The  connection  occasionally  established 
between  the  superficial  middle  cerebral  vein  and  the  transverse 
sinus  is  called  the  posterior  anastomotic  vein;  wiiile  the  great  anas- 
tomotic vein  (of  Trolard)  is  produced  when  it  joins  one  of  the 
superior  cerebral  veins.  The  great  anastomotic  vein  connects 
the  superior  sagittal  with  the  cavernous  sinus. 

There  are  no  lymphatic  vessels  in  either  the  brain  or  spinal 


24  THE    MENINGES    OF    THE    BRAIN. 

cord;  perivascular  lymph  spaces  carry  the  fluid  from  the  interior 
to  the  subarachnoid  spaces. 

B.     THE  CIRCULATION  OF  THE  RHOMBENCEPHALON. 

Bl.  The  medulla  oblongata  is  supplied  with  blood  by  the 
following  branches  of  the  vertebral  artery:  The  posterior  and 
the  anterior  spinal,  the  posterior  inferior  cerebellar  and  several 
short  bulbar  arteries  (Fig.  9).  The  posterior  inferior  cerebellar 
(a.  cerebelli  inferior  posterior)  winds  from  before  backward  around 
the  medulla,  runs  between  the  vagus  and  accessory  nerves,  enters 
the  vallecula  cerebelli-  and  gives  branches  to  the  medulla  and  to 
the  chorioid  tela  of  the  fourth  ventricle.  The  anterior  spinal 
artery  (a.  spinalis  anterior)  formed  by  the  y-like  union  of  a  branch 
from  each  vertebral  artery,  descends  along  the  anterior  median 
fissure;  and  the  posterior  spinal  artery  {a.  spinalis  posterior)  of 
either  side,  rising  from  the  vertebral  near  the  lower  end  of  the 
medulla,  descends  in  front  of  the  posterior  lateral  sulcus.  Both 
distribute  branches  along  their  course.  The  branches  for  the 
most  part  enter  the  median  raphe  or  follow  the  roots  of  the  bulbar 
nerves,  suggesting  the  centrifugal  and  centripetal  arteries  of  the 
spinal  cord  (Fig.  13).  The  veins  pursue  much  the  same  course 
as  the  arteries.  The  anterior  median  vein  joins  the  ventral  veins 
of  the  pons  and  is  drained  into  the  cerebellar  veins  or  directly 
into  the  superior  petrosal  sinus.  The  posterior  median  vein  bifur- 
cates y-like  at  the  middle  of  the  medulla  and  the  two  branches 
wind  around  the  medulla  to  its  anterior  surface  and  empty  into 
the  inferior  petrosal  sinus  or  the  basilar  plexus.  Issiiing  from 
the  medulla  vrith  the  roots  of  the  ninth  to  the  twelfth  cerebral 
nerves  are  three  or  four  small  veins,  the  radicular  veins,  which 
run  into  the  occipital  and  inferior  petrosal  sinuses  (Cunningham). 
Both  arteries  and  veins  possess  perivascular  lymph  spaces,  but 
there  are  in  the  medulla  no  lymphatic  vessels. 

B2.  The  pons  Varolii  is  supplied  by  the  pontal,  the  supe- 
rior cerebellar  and  the  posterior  cerebral  branches  of  the  basilar 
artery  (Fig.  9).  The  short  and  transverse  branches  of  the  basilar 
artery,  the  pontal  arteries  {aa.  pontales),  furnish  the  greater  portion 
of  blood  to  the  basilar  area  of  the  pons,  while  the  superior  cere- 


THE    CIRCULATION    OF    THE    RHOMBENCEPHALON. 


25 


E 

o 
o 

<  c 


15  E 


C.C 


5  = 


3  E 


THE    CIRCULATION    OF    THE    RHOMBENCEPHALON. 


27 


bellar  artery  supplies  the  superior  medullary  velum  and  the 
brachia  conjunctiva  cerebelli.  The  branches  enter  the  median 
raphe,  also  the  substance  of  the  pons  elsewhere,  especially  along 
the  nerve  roots,  and  run  at  right  angles  to  the  surface  into  it. 
The  deep  veins  of  the  pons  run  forward  and  form  a  plexus  on  its 
surface  which,  according  to  Cunningham,  is  drained  by  a  superior 
efferent  into  the  basilar  vein  and  by  an  inferior  efferent  into  the 
cerebellar   veins   or   the   superior  petrosal  sinus.     There  are  no 


d.spm.Tioit 


ut.rtel>7 


Fig.  1 3. — Arteries  of  the  medulla  oblongata.     (Modified  from  Gordinier  after  Diiret.) 

a.spin.post.  Posterior  spinal  artery,     a.vertebr.  Vertebral  artery,     a. spin. ant.  Anterior  spinal 

artery. 

lymphatic  vessels  in  the  pons;  but,  as  elsewhere  in  the  central 
nervous  system,  there  are  lymph  spaces  about  the  blood-vessels. 

B3.  The  blood  supply  of  the  cerebellum  is  furnished  by 
three  pairs  of  arteries  (Fig.  9).  The  superior  cerebellar,  from 
the  basilar,  supplies  all  the  superior  surface  except  a  narrow  zone 
at  the  posterior  border;  the  anterior  inferior  cerebellar,  also  from 
the  basilar,  and  the  posterior  injerior  cerebellar,  from  the  verte- 
bral, supply  the  inferior  surface  and  the  posterior  part  of  the 
superior  surface. 

The  Superior  Cerebellar  Artery.  (.4.  cerebelli  superior). — 
Rising  from  the  basilar  just  behind  the  posterior  cerebral,  from 


28 


THE    MENINGES    OF    THE    BRAIN. 


which  it  is  separated  by  the  oculomotor  nerve,  it  winds  dorsally 
around  the  mid-brain  to  the  sulcus  lateralis,  where  it  bifurcates 
into  a  medial  and  a  lateral  branch  (Fig.  9).  The  medial  branch 
continues  along  the  trochlear  nerve  in  the  groove  between  the 
cerebellum  and  the  mid-brain  almost  to  the  median  line ;  and  then, 
bending  backward,  runs  along  the  superior  worm  of  the  cere- 
bellum to  its  posterior  extremity.  It  distributes  branches  to 
the    geniculate    bodies,    corpora    quadrigemina,    tela    chorioidea 


ivz 


iVi 


in 


02  ; 


Ui 


Fig.  14. — Median  section  of  embryonic  brain  of  the  third  month. 
{McMurrich  after  His.) 

I.  Myelencephalon.  II.  Metencephalon:  i,  Pons,  2,  Cerebellum.  III.  Isthmus  rhomb- 
encephali.  IV.  Mesencephalon:  i ,  Pedunculi ,  2,  Corpora  quadrigemina.  V.  Diencephalon: 
I,  Pars  mammillaris  hypothalami,  2,  Thalamus,  3,  Epithalamus.  VI.  Telencephalon:  1,  Pars 
optica  hypothalami,  2,  Corpus  striatum,  3,  Rhinencephalon,  4,  Neopallium. 

ventriculi  tertii  and  posterior  surface  of  the  pons,  besides  the 
vermis  superior  cerebelli  and  the  medial  part  of  the  superior 
surface  of  the  hemisphere.  The  lateral  branch  of  the  superior 
cerebellar  artery  passes  from  its  point  of  origin  near  the  sulcus 
lateralis  of  the  mid-brain  onto  the  superior  surface  of  the  cere- 
bellum. It  runs  backward  a  half-inch  from  the  border  of  that 
surface,  giving  off  collaterals  along  its  course.  The  lateral  branch, 
together  with  the  medial,  supplies  the  superior  cerebellar  surface 
almost  as  far  back  as  the  horizontal  sulcus  of  the  cerebellum, 
along  which  the  superior  cerebellar  artery  anastomoses  with  both 
the  inferior  cerebellar  arteries. 


THE    CIRCULATION    OF   THE    RHOMBENCEPHALON.  29 

The  anterior  inferior  cerebellar  artery  (a.  cerehelli  anterior 
inferior,  Fig.  9)  is  given  off  by  the  basilar  near  the  junction  of 
its  inferior  and  middle  thirds.  (Sometimes  it  is  replaced  by 
two  or  three  small  vessels.)  It  runs  lateralward,  behind  the 
flocculus,  keeping  close  to  the  anterior  border  of  the  hemisphere. 
In  its  course  it  passes  anterior  to  the  abducent  nerve  and  posterior 
to  the  facial  and  auditory  nerves.  It  supphes  the  anterior  part 
of  the  under  surface  and  border  of  the  cerebellar  hemisphere. 

The  posterior  inferior  cerebellar  artery  (a.  cerehelli  inferior 
posterior,  Fig.  9)  is  the  largest  branch  of  the  vertebral  and  is  given 
off  just  before  the  vertebral  arteries  unite  and  form  the  basilar. 
Passing  first  between  the  root-bundles  of  the  hypoglossal  nerve 
and  then  betw^een  those  of  the  accessory  and  vagus  nerves,  the 
posterior  inferior  cerebellar  artery  bends  at  a  right  angle  back- 
ward and  runs  between  the  medulla  and  the  cerebellar  hemisphere, 
where  it  divides  into  a  medial  and  a  lateral  branch.  The  medial 
branch  follows  the  sulcus  valleculse  and  gives  branches  to  the 
medial  part  of  the  hemisphere  and  the  vermis  inferior.  It  anas- 
tomoses mth  its  fellow  of  the  opposite  side.  The  lateral  branch, 
runs  lateralward  from  the  posterior  cerebellar  notch  over  the 
inferior  surface  of  the  hemisphere;  its  terminal  branches  \s"ind 
around  the  postero-lateral  border  and  communicate  with  the 
superior  cerebellar  artery  on  the  upper  surface  of  the  hemisphere. 
The  undinded  trunk  of  the  posterior  inferior  cerebellar  artery 
gives  small  branches  to  the  medulla  oblongata  and  suppHes  the 
chorioid  tela  of  the  fourth  ventricle. 

The  internal  cerebellar  veins  bring  the  blood  from  the  interior 
of  the  organ  and  pour  it  into  the  superior  and  inferior  external  veins. 

The  superior  external  cerebellar  veins  (vencB  cerebelll  supe- 
riores)  converge  forward  into  a  medial  vein,  which  empties  into 
the  great  cerebral  vein,  and  several  lateral  veins,  which  end  in  the 
transverse  or  the  superior  petrosal  sinus. 

The  inferior  external  cerebellar  veins  (vence  cerehelli  inje- 
riores)  also  form  one  small  medial  vein,  which  runs  backward 
and  upward  either  into  the  straight  or  transverse  sinus,  and  a 
number  of  lateral  veins.  The  lateral  inferior  cerebellar  veins 
terminate  in  the  inferior  petrosal  and  in  the  occipital  sinus. 


THE    MENINGES    OF    THE    BRAIN. 


Lymphatics. — ^There  are  no  lymphatic  vessels  in  the  cere- 
bellum, but  the  perivascular  lymph  spaces  carry  out  the  lymph 
and  pour  it  chiefly  into  the  subarachnoid  space. 


TABLE  I. 

EMBRYOLOGIC  DIVISIONS  OF  THE  BRAIN. 

In  accordance  with  its  development  the  brain  or  encephalon 
is  naturally  divided  into  three  embryologic  divisions  which  com- 
prise the  derivatives  of  the  anterior,  the  middle  and  the  poste- 
rior brain- vessels  (Fig.  14). 

[  Cerebral  Hemispheres 
Corpus  Callosum 
Fornix 

Anterior  Commissure 
Septum  Pellucidum 
Lamina  Terminalis 
Tuber  Cinereum 
Optic  Chiasma  (grows 

into  it) 
Lateral  Ventricles 
Foramina  interventric- 

ularia 
I  Aula  of  third  Ventricle. 


I.  Fore-Brain,  or 
Prosencephalon 
(Ant.  vesicle) 


I.  End-brain,  or 
Telencephalon 


2.  Inter -brain,  or 
Diencephalon 


Cerebrum  < 


II.  Mid-Brain,  or 
Mesencephalon 
(Middle  vesicle) 


I.  Pedunculi 
Cerebri 


2.  Lamina 

Quadrigemina 


Thalami 

Corpora  Mammillaria 
Corpus  Pineale 
Corpora  Geniculata 
Third    Ventricle,    ex- 
cepting the  aula. 

Bases  Pedunculi 
Substantia  Nigra 
Tegmenta 

Cerebral  Aqueduct  (of 
Sylvius) 

Corpora     Quadrigem- 
ina. 
Brachia. 


EMBRYOLOGIC    DIVISIONS    OF    THE    BRAIN. 


31 


--  Prosenceph- 
alon, (fore- 
brain) 


r  Cerebrum 


i!     ' ''  r  ~  "  ~  ~  -  -  _  Mesencephalon 
{mid-braiu) 


01ivary_body , 


*  -  Cere-     1 

helium  I  Metencephalon 


r     (hind-brain)      \  Rhomben- 
Pons  (Varolii)   J 


Myelencephalon 
(Medulla  oblongata) 


1-   cephalon 


Encephalon 
(brain) 


'  Pars  cervicalis  1 


"  Pars  thoracalis 


Pars  lumbalis 


\\,       Pars  sacralis  or 
'  conus  medullaris 


Spinal  cord 
(medulla  spinalis) 


Fig.  15. — Divisions  of  the  brain.     Diagrammatic.     (After  Morris's  Anatomy.) 


III.  Rhombencephalon 
(Post,  vesicle) 


EMBRYOLOGIC    DIVISIONS    OF   THE   BRAIN.  33 

I  Isthmus  Rhombencephali 

.  Metencephalon     j  Cerebellum,  Pons 

(Hind-brain)         I  Upper  half  of  Fourth  Ven- 
'^       tricle 


2.  Myelencephalon    f  ^^^^"^  Oblongata 

<   Lower  half  of  Fourth  Ven- 


(After-brain) 


tricle 


The  cerebrum  embraces  the  jore-hrain  and  the  mid-hrain,  as 
shown  by  the  table.  So  we  may  make  a  more  comprehensive 
division  of  the  brain  into  only  two  grand  di\dsions:  The  great 
brain  or  cerebrum  and  the  rhombencephalon  (Fig.  15).  We  may 
now  simpHfy  the  above  table  as  follows : 

I.  Cerebrum,  embracing — 

End-brain,  or  Cerebral  Hemispheres,  etc.  ' 

Inter-brain  '  : 

Mid-brain. 

II.  Rhombencephalon,  comprising — 
Isthmus 

Cerebellum 

Pons 

Medulla  Oblongata. 


CHAPTER  II. 

GENERAL  CONSIDERATIONS  OF  THE  BRAIN  OR 
ENCEPHALON. 

Before  taking  up  the  special  study  of  the  cerebrum  the  student 
should  notice  certain  prominent  features  of  the  entire  brain.  To 
do  this  the  arachnoid  and  pia  mater  must  be  removed,  and  great 
care  and  patience  should  be  exercised  to  preserve  the  integrity 
of  the  brain  substance  and  to  guard  against  evulsion  of  the  roots 
of  the  cerebral  nerves. 

The  human  brain  forms  the  greatly  expanded  superior  extrem- 
ity of  the  cerebro-spinal  axis.  It  is  derived  from  three  sack-like 
dilatations  of  the  epiblastic  neural  tube,  called  the  anterior,  the 
middle  and  the  posterior  brain- vesicles  (Fig.  i6). 

Cavities. — ^The  cavities  of  these  brain-vesicles  constitute  the 
adult  ventricles,  which  form  a  continuous  median  series  extend- 
ing from  the  canal  of  the  spinal  cord  up  to  the  level  of  the 
cerebral  hemispheres;  at  that  level  the  central  cavity  bifurcates 
into  a  branch  for  each  hemisphere  of  the  cerebrum  (Figs.  17  and 
18).  Thus  is  formed  the  lateral  ventricle  in  the  cerebral  hemis- 
phere and,  below  the  cerebral  hemispheres,  the  median  series  of 
cavities  comprises  the  third  ventricle  in  the  inter-brain,  the  cerebral 
aqueduct  in  the  mid-brain,  and  the  fourth  ventricle  in  the  hind- 
brain  and  after-brain.  The  walls  of  these  simple  embryonic 
ca\aties  undergo  wonderful  development  and  speciaHzation; 
ultimately  they  produce  all  the  multiform  and  complicated  struc- 
tures of  the  adult  human  brain. 

Superior  View. — ^The  superior  surface  of  the  brain  is  markedly 
convex  (Figs.  19  and  22).  It  is  elhptical  in  outHne,  the  major 
axis  being  contained  in  the  median  line;  the  greatest  transverse 
axis  is  situated  a  little  behind  the  middle  and  runs  between  the 
points  which,  when  the  brain  is  in  the  skull,  underlie  the  tubera 
parietalia.     This  surface  is  closely  adapted  to  the  interior  of  the 

34 


CONSIDERATIONS    OF    THE    BRAIN    OR    ENCEPHALON. 


35 


calvaria.  Only  the  great  convoluted  hemispheres  of  the  cerebrum 
are  visible  from  the  superior  ^de^v-point.  The  two  hemispheres 
are  separated  by  a  deep,  median  cleft,  called  the  longitudinal 
fissure  of  the  cerebrum  (fissura  longitudinalis  cerebri)  from 
which  the  falx  cerebri  has  been  removed. 

Posterior  View. — ^\Vhen  the  brain  is  viewed  from  behind,  three 
great  structures  and  two  transverse  fissures  are  visible  (Fig.  20): 


Fig.  16. — Diagrams  of  surface  \-iews  and  sections  of  germinal  areas  sho-5\'ing 
the  development  of  the  primitive  streak,  neural  groove,  neural  tube  and  brain 
vesicles.     (Mter  Morris's  Anatojny.) 

A.  Earlier  'stage,  a.  Germinal  area.  b.  Neural  groove,  c.  Primitive  streak.  B.  Later 
stage,  a.  Germinal  area.  b.  Fore-brain  (rudiment  of  cerebral  hemispheres),  c.  Optic  vesicle, 
d.  First  cerebral  vesicle,  e.  Second  cerebral  vesicle,  f.  Third  cerebral  vesicle.^  g.  Primitive 
streak.  A'.  Section  through  area  A  along  the  line  a.  a.  Germinal  area.  b.  Xeural  groove. 
B'.  Section  through  area  B  along  line  h.    a.  Germinal  area.    b.  Neural  crest,    c.  Neural  tube. 


First,  the  occipital  end  of  the  cerebral  hemispheres  with  their 
irregular  gyri  and  sulci;  second,  the  transversely  laminated  cere- 
bellum, Iving  below  the  cerebrum  and  separated  from  it  by  the 
transverse  fissure  of  the  cerebrum  (fissura  transversa  cerebri); 
and  third,  the  inferior  extremity  of  a  relatively  small  median 
structure,  the  medulla  oblongata.     The  cerebellum  is  especially 


36 


CONSIDERATIONS    OF    THE    BRAIN    OR    ENCEPHALON. 


characterized  by  its  parallel  crescentic  sulci,  which  give  it  a  strati- 
fied appearance.  It  shows  a  partial  subdi\dsion  into  lateral 
hemispheres  produced  by  a  posterior  median  depression,  called 
the  posterior  cerebellar  notch,  and  by  a  longitudinal  groove  on  its 
inferior  surface,  called  the  vallecula  cerebelli.  The  vallecula  is 
fitted  over  the  posterior  surface  of  the  medulla.  The  cerebellum 
is,  therefore,  separated  from  the  medulla  oblongata  by  a  sharply 


Fig.  17. — Diagrammatic  horizontal  section  of  vertebrate  brain. 
(Morris's  Anatomy  after  Huxley.) 

a.  Metencephalon.  b.  Thalamus,  c.  Medulla  oblongata,  d.  Cerebellum,  e.  Lateral  ven- 
tricle, f.  Olfactory  diverticulum,  g.  Lamina  terminalis.  h.  Corpus  striatum,  i.  Mid-brain. 
j.  Pineal  body.    k.  Interventricular  foramen. 


curved,  rainbow-shaped  fissure.  That  fissure  is  the  transverse 
fissure  of  the  cerebellum  (fissura  transversa  cerebelli)  which,  as 
already  pointed  out,  is  bridged  over  by  the  arachnoid  and  con- 
tains the  cisterna  cerebello-medullaris. 

Inferior  View. — ^The  base  of  the  brain  presents  three  areas, 
situated  in  three  successive  levels,  which  correspond  in  location 
and  extent  to  the  great  fossce  in  the  base  of  the  cranium  (Figs.  21 
and  27).  The  anterior  area,  situated  in  the  anterior  cranial  fossa, 
occupies  the  highest  level;  the  middle  area  is  intermediate  in 
position;  it  occupies  the  middle  fossa  and  together  with  the  anterior 
area  comprises  all  of  the  base  of  the  cerebrum  which  is  visible  in 
the  complete  brain;  and,  the  posterior  area,  which  is  but  the  base 
of  the  rhombencephalon,  is  situated  at  the  lowest  level  in  the 
posterior  fossa  of  the  cranium. 

The  anterior  area  of  the  base  of  the  brain  is  divided  into 
lateral  halves  by  the  longitudinal  fissure  of  the  cerebrum,  and 


CONSIDERATIONS    OF    THE    BRAIN    OR    ENCEPHALON. 


37 


separated  from  the  middle  area  by  the  fossa  and  fissura  lateralis 
cerebri.  The  frontal  lobe  of  the  cerebral  hemisphere,  on  either 
side  of  the  longitudinal  fissure,  makes  up  nearly  all  this  area. 
The  inferior  surface  of  the  frontal  lobe  is  concave  and  is  adapted 
to  the  convex  orbital  plate  of  the  frontal  bone;  its  medial  border 
is  most  prominent  and  presents,  near  the  longitudinal  fissure,  an 
elongated  gray  mass,  the  olfactory  bulb  (if  it  has  not  been  torn 


k  1  tn  n  o 

Fig.  i8. — Diagrammatic  sagittal  section  of  vertebrate  brain. 

(Morris's  Anatomy  after  Huxley.) 

a.  Corpora  quadrigemina.  b.  Mid-brain,  c.  Pineal  body.  d.  Cerebellum  (hind-brain). 
e.  Medulla  oblongata  (after-brain),  f.  Pons  Varolii  (hind-brain),  g.  Lateral  ventricle. 
h.  Cerebral  hemisphere,  i.  Corpus  striatum,  j.  Olfactory  diverticulum,  k.  Pedunculi 
cerebri.  1.  Thalamus,  m.  Inter-brain,  n.  Hypophysis,  o.  Interventicular  foramen.  4. 
Fourth  ventricle,     s.  Aqueduct  of  cerebrum.     3.  Third  ventricle. 

oft")  and  a  white  strand,  the  olfactory  tract.  Running  backward 
from  the  bulb,  parallel  with  the  longitudinal  fissure  of  the  cere- 
brum to  the  fossa  lateraHs  cerebri,  the  olfactory  tract  is  seen  to 
bifurcate  into  two  distinct  striae,  a  medial  and  a  lateral. 

The  middle  area  of  the  inferior  surface  of  the  brain  is  prom- 
inent laterally  where  it  is  formed  by  the  temporal  lobes  of 
the  cerebrum.  It  is  depressed  in  its  median  portion  and  thus 
adapted  to  the  hypophyseal  region  of  the  cranial  floor.  This 
median  hypophyseal  region  extends  from  the  end  of  the  longit- 
udinal fissure,  in  front,  backward  to  a  great  white,  transversely 
striated  eminence,  called  the  pons;  it  contains  several  important 
structures,  viz.,  the  bases  pedunculi;  posterior  perforated  sub- 
stance; the  mammillary  bodies;  tuber  cinereum  and  stem  of  the 
inf undibulum ;  optic  chiasma,  tracts  and  nerves;  lamina  cinerea 
terminalis;  and  the  anterior  perforated  substance. 

Issuing  from  the  under  surface  of  the  cerebral  hemisphere  and 


38  CONSIDERATIONS    OF   THE    BRAIN    OR   ENCEPHALON. 

running  downward  toward  the  median  line,  there  may  be  seen  a 
white  striated  band,  a  half-inch  broad,  called  the  basis  pedunculi, 
which,  on  approximating  its  fellow  in  the  median  plane  disappears 
into  the  pons.  Anteriorly,  the  X-Hke  optic  chiasma  (chiasma 
opticum)  is  easily  identified  near  the  longitudinal  fissure;  its  ante- 
rior limbs  are  the  optic  nerves  and  its  posterior,  the  optic  tracts 
(Fig.  21).  The  optic  tract,  when  traced  backward  and  out- 
ward, under  the  overhanging  temporal  lobe,  is  observed  to  cross 
the  basis  pedunculi  at  its  point  of  emergence  from  the  cerebral 
hemisphere.  Thus  the  optic  tract  and  the  basis  pedunculi  form 
the  lateral  boundary  of  a  diamond- shaped  space  extending  from 
the  optic  chiasma,  in  front,  backward  to  the  pons.  This  is  com- 
monly called  the  interpeduncular  space.  You  observe  in  it  three 
structures:  (i)  A  gray  eminence  just  behind  the  optic  chiasma 
called  the  tuber  cinereum;  (2)  a  pair  of  white,  nipple-like  bodies, 
an  eighth  of  an  inch  in  diameter,  known  as  the  zvhite  or  mammil- 
lary  bodies  {corpora  mammillaria),  and  (3)  a  triangular,  perforated 
mass  of  dark  gray  substance,  called  the  posterior  perforated  sub- 
stance {substantia  perforata  posterior).  In  the  normal  condition, 
the  infundibulum  projects  downward  and  forward  from  the  center 
of  the  tuber  cinereum  and  connects  it  with  the  hypophysis  cerebri; 
but  it  is  usually  broken  in  removing  the  brain  and  the  hypophysis 
left  behind  in  the  hypophyseal  fossa. 

If  the  optic  chiasma  be  drawn  slightly  downward  and  back- 
ward, a  transverse  and  nearly  vertical  sheet  of  gray  matter  will 
be  seen  extending  upward  from  it,  between  the  cerebral  hemis- 
pheres, toward  the  corpus  callosum.  That  is  the  lamina  cinerea 
terminalis.  It  bounds  posteriorly  the  frontal  part,  of  the  longit- 
udinal fissure  of  the  cerebrum.  Lateral  to  the  optic  chiasma 
and  anterior  to  the  optic  tract,  the  gray  substance  is  perforated 
by  many  vessels;  it  is  called  the  anterior  perforated  substance 
{substantia  perforata  anterior)  to  distinguish  it  from  a  similar 
posterior  region  located  between  the  bases  pedunculi. 

Posterior  Area. — ^The  posterior  area  of  the  base  of  the  brain 
is  formed  by  the  pons,  the  cerebellum,  and  the  medulla  oblongata, 
which  constitute  the  rhombencephalon  (Fig.  21).  The  pons 
and  medulla  are  median  structures.     They  are  separated  by  a 


CONSIDERATIONS    OF    THE    BRAIN    OR    ENCEPHALON.  39 


Fig.  19. — Fronto-superior  surface  of  cerebrum.     (Original.) 


CONSIDERATIONS    OF   THE    BRAIN    OR   ENCEPHALON.  4 1 

well  marked  transverse  groove  containing  the  roots  of  the  sixth, 
the  seventh,  the  intermediate  and  the  eighth  cerebral  nerves. 
The  trans\'erse  strands  of  the  pons  traced  laterahvard  are  obser\-ed 
to  form  a  large  round  bundle,  called  the  brachium  poniis,  which 
extends  into  the  hemisphere  of  the  cerebellum  on  either  side.  Be- 
tween those  pontine  strands,  at  the  lateral  border  of  the  pons, 
there  should  be  noticed  the  roots  of  the  great  trigeminal  nerve. 
A  sagittal  hne  through  this  nerve  at  its  attachment  to  the  pons 
may  be  regarded  as  the  boundary  between  the  pons  and  the  cere- 
bellar hemisphere.  The  hemispheres  of  the  cerebellum  form  the 
lateral  part  of  the  posterior  area;  their  stratified  appearance  is 
already  familiar.  Inferior  to  the  pons  is  the  medulla  oblongata. 
The  medulla  is  about  an  inch  long  and  three-quarters  of  an  inch 
broad  near  the  pons,  but  measures  less  than  one-half  inch  in 
width  at  the  lower  end.  It  is  partially  divided  into  lateral  halves 
by  the  anterior  median  fissure,  which  is  deep,  above,  but  is  almost 
obliterated  in  the  lower  half  of  the  medulla  by  the  crossing  of  the 
lateral  pyramidal  tracts,  the  decussatio  pyramidum.  On  either 
side  of  the  anterior  median  fissure,  the  student  should  notice,  in 
this  order,  the  pyramid,  the  olive,  and  the  restiform  body.  The 
pyramid  (pyramis)  bounds  the  anterior  median  fissure.  It  is 
an  eighth  of  an  inch  in  width,  is  most  prominent  near  the  pons 
and  tapers  off  inferiorly  because  about  80  per  cent,  of  its  fibers 
cross  over  to  the  opposite  side  and  sink  backward  in  the  medulla. 
It  is  bounded  laterally  by  a  slight  longitudinal  furrow,  the  anterior 
lateral  sulcus  (sulcus  lateralis  anterior)  which  contains  the  roots 
of  the  twelfth  cerebral  nerve,  and  separates  the  pyramid  from  the 
olive  and  from  a  flat  surface,  called  the  lateral  funiculus  of  the 
medulla.  The  olive  (oliva)  occupies  the  upper  half  of  the  lateral 
surface  of  the  medulla;  the  lateral  funiculus,  the  lower  half. 
The  olive  is  equal  in  breadth  to  the  pyramid.  It  is  quite  promi- 
nent, is  white  in  color  and  is  elliptical  in  outline.  The  posterior 
lateral  sulcus  (sulcus  lateralis  posterior)  separates  it  from  the 
restiform  body.  The  roots  of  the  ninth,  tenth  and  eleventh  cere- 
bral nerves,  which  are  contained  in  that  groove  and  the  restiform 
body  which  lies  beyond  it,  can  be  seen  only  by  pressing  aside 
the  hemisphere  of  the  cerebellum. 


42  CONSIDERATIONS    OF    THE    BRAIN    OR    ENCEPHALON. 

The  Roots  of  the  Twelve  Cerebral  Nerves  (Fig.  21).— The 
cerebral  nerves  (nervi  cerebrales)  are  numbered  from  before  back- 
ward according  to  the  order  of  their  points  of  attachment  to  the 
brain  surface.  Those  points  of  attachment  are,  for  the  motor 
roots,  points  of  exit  from  the  brain  (apparent  origins);  and  are 
points  of  entrance  into  the  brain  (apparent  central  terminations), 
for  all  the  sensory  roots.  The  genetic  nucleus  {nucleus  originis), 
which  is  the  real  origin  of  each  motor  root,  and  the  terminal 
nucleus  {nucleus  terminalis),  which  contains  the  real  central  ter- 
mination of  every  sensory  root,  are  imbedded  within  the  brain 
substance  and  do  not  at  present  concern  us. 

1.  The  olfactory  nerves  {nervi  olfactorii)  are  the  first.  They 
are  the  nerves  of  smell.  They  are  composed  of  twenty  or  thirty 
scattered  bundles  of  non-medullated  fibers  which  rise  from  the 
olfactory  cells  in  the  nasal  mucous  membrane  and,  passing  through 
the  cribriform  plate  of  the  ethmoid  bone,  enter  the  under  surface 
of  the  olfactory  bulb.  The  surface  of  the  bulb  is,  therefore, 
their  apparent  central  termination.  The  fibers  proceed  some 
distance  into  the  gray  substance  of  the  olfactory  bulb,  which 
constitutes  the  terminal  nucleus  of  the  first  nerves,  and  there 
branch  richly  and  end  in  relation  with  the  mitral  and  bush-cells 
(real  central  termination). 

2.  Optic  Nerve.  {Nervus  opticus). — ^The  second  nerve,  the 
nerve  of  sight,  is  really  a  brain  tract  rather  than  a  nerve,  and 
its  fibers  are  imbedded  in  neuroglia.  It  rises  in  the  ganglionar 
layer  of  the  retina.  Passing  through  the  chorioid  and  sclera  of 
the  eyeball  and  the  optic  foramen  of  the  sphenoid  bone,  it  enters 
into  the  optic  chiasma  where  the  "nerve"  is  said  to  end;  but  the 
fibers  of  the  nerve  continue  without  interruption  through  the 
optic  tracts  and  their  lateral  roots  to  the  inter-brain  and  the  mid- 
brain, whose  surfaces  they  pierce  {apparent  central  termination); 
they  end  (real  central  termination)  in  the  lateral  geniculate  body, 
in  the  pulvinar  of  the  thalamus,  and  in  the  superior  colliculus  of 
the  quadrigeminal  bodies. 

3.  The  oculomotor  nerve  {n.  oculomotorius)  is  the  great  motor 
nerve  to  the  eye  (Fig.  21).  It  issues  from  the  mid-brain  at  the 
medial  border  of  the  basis  pedunculi,  which  is  its  apparent  origin, 


CONSIDERATIONS    OF   THE    BRAIN    OR    ENCEPHALON.  43 


Fig.  20. — Posterior  view  of  the  brain.     (Original.) 


CONSIDERATIONS    OF   THE    BRAIN    OR    ENCEPHALON.  45 

but  its  real  origin  is  in  a  mass  of  gray  substance,  the  genetic 
nucleus  (n.  originis),  situated  within  the  depths  of  the  mid-brain. 

4.  Trochlear  Nerve.  (N.  Irochlearis). — The  fourth  is  a  motor 
nerve  to  the  eye  and  is  the  smallest  of  the  cerebral  nerves.  It 
may  be  seen  winding  forward  over  the  basis  pedunculi  (Fig.  21). 
Its  apparent  origin  is  from  the  dorsal  surface  of  the  brain  stem 
at  the  junction  of  the  mid-brain  with  the  hind-brain  (the  isthmus, 
Fig.  44) ;  this  apparent  origin  cannot  be  seen  in  the  complete  brain. 
The  genetic  nucleus  of  the  fourth  nerve  is  located  below  that 
of  the  third  in  the  mid-brain. 

5.  Trigeminal  Nerve.  (N.  trigeminus).— The  trigeminal  nerve 
is  a  mixed  nerve,  motor  and  sensory  (Fig.  21).  It  is  attached 
to  the  ventral  surface  of  the  pons  a  little  above  the  middle  of  its 
lateral  border.  The  small  anterior  motor  root  emerges  from 
this  point  (apparent  origin) ;  but  this  is  the  apparent  central  termina- 
tion of  the  large  sensory  root,  which  rises  in  the  semilunar  gang- 
lion (Gasseri)  and  enters  the  pons  close  to  the  emergence  of  the 
motor  root. 

6.  The  abducent  nerve  (n.  abducens)  is  a  motor  nerve  to 
the  eye.  It  issues  from  the  pons  at  its  inferior  border,  or  from 
the  transverse  groove  between  the  pons  and  the  medulla,  just 
above  the  pyramid  of  the  medulla  and  nearly  in  line  with  the 
anterior  lateral  sulcus  (Fig.  21). 

In  the  transverse  groove  between  the  pons  and  the  meduUa, 
lateralward  from  the  root  of  the  sixth  nerve,  are  the  roots  of  the 
seventh,  intermediate  and  eighth.  The  seventh  is  smaller  in 
diameter  than  the  eighth  and  medial  to  it  in  position;  the  inter- 
mediate is  between  these  two  (Figs.  21  and  45). 

7.  The  facial  nerve  (n.  facialis)  is  the  motor  nerve  to  the 
muscles  of  expression  (Figs.  21  and  45).  Rising  from  a  nucleus 
in  the  pons,  its  emergence  from  the  transverse  groove  between  the 
medulla  and  pons  constitutes  its  apparent  origin.  The  inter- 
mediate nerve  (n.  intermedins)  is  so  closely  associated  with  the 
facial  nerve  that  many  regard  it  as  the  sensory  root  of  that  nerve; 
but  the  intermediate  nerve  is  in  reality  a  mixed  nerve  with  efferent 
fibers  of  vasodilator,  secretory  and  trophic  functions  and  afferent 
fibers  whose  function  is  taste.     The  efferent  fibers  rise  from  the 


46  CONSIDERATIONS    OF    THE    BRAIN    OR    ENCEPHALON. 

salivary  nucleus  (the  dorsal  part  of  the  facial  nucleus)  in  the 
pons.  They  issue  from  the  transverse  ponto-meduUary  groove 
between  the  facial  and  auditory  nerves  {apparent  origin)  at  the 
point  where  the  afferent  fibers  enter  the  brain.  The  sensory 
part  of  the  intermediate  nerve,  which  is  the  nerve  of  taste  to  the 
anterior  part  of  the  tongue,  takes  its  origin  in  the  ganglion  geniculi 
situated  within  the  canalis  facialis  (FoUopii);  its  apparent  central 
termination  is  in  the  ponto-medullary  groove. 

8.  The  acustic  nerve  {n.  acusticus)  is  a  sensory  nerve,  having 
the  double  function  of  hearing  and  equilibrium  (Figs.  21,  44 
and  45).  It  rises  from  the  spiral  and  vestibular  ganglia  situated 
in  the  petrous  bone,  and  its  apparent  central  termination  is  in  the 
bottom  of  the  transverse  groove  separating  the  pons  from  the 
medulla.  The  roots  of  both  the  seventh  and  eighth  nerves  are 
near  the  upper  end  of  the  posterior  lateral  sulcus  of  the  medulla 
oblongata. 

9.  Glossopharngeal  Nerve.  {N.  glossopharyngeus). — ^This 
is  a  complex  mixed  nerve,  containing  efferent  fibers  (motor,  vaso- 
dilator, secretory  and  trophic)  and  afferent  fibers,  which  are  both 
common  sensory  and  gustatory.  It  is  joined  to  the  medulla  in 
the  bottom  of  -the  superior  end  of  the  posterior  lateral  sulcus 
(Figs.  21  and  45).  This  point  of  attachment  is  the  apparent 
origin  of  its  efferent  and  the  apparent  central  termination  of  its 
afferent  fibers.  The  latter  fibers  rise  in  the  superior  and  petrosal 
glossopharyngeal  ganglia  situated  in  the  jugular  foramen.  The 
genetic  nucleus  of  the  efferent  fibers  is  located  inside  the  medulla. 

Behind  the  ninth  nerve  in  the  same  groove  are  the  roots  of  the 
tenth  and  eleventh  nerves.  The  roots  of  the  ninth  and  tenth 
are  situated  between  the  olive  and  the  restiform  body;  but,  if  the 
nerve  trunks  have  been  cut,  it  is  impossible  to  determine  which 
of  the  ten  or  a  dozen  root  bundles  belong  to  each  of  them. 

10.  The  Vagus  Nerve.  {N.  vagus). — ^The  efferent  fibers  of  the 
vagus,  like  the  glossopharyngeal,  take  their  apparent  origin  from 
the  posterior  lateral  sulcus,  and  in  the  same  sulcus  the  afferent 
fibers  enter  the  medulla,  apparent  central  termination  (Figs.  21 
and  45).  It  is  a  very  complex  nerve.  Its  efferent  fibers  comprise 
motor,  inhibito-motor,  vasodilator,  secretory,  trophic  and  inhibito- 


CONSIDERATIONS    OF    THE    BRAIN    OR    ENCEPHALON. 


47 


Fig.  21. — Base  of  brain.     {Original.) 

a.  Olfactory  bulb.  b.  Olfactory  tract,  c.  Medial  and  lateral  olfactory  striae,  d.  Trigo- 
num  olfactorium.  e.  Area  parolfactoria  (Brocae).  f.  Anterior  perforated  substance,  g.  Op- 
tic chiasma.  h.  Optic  tract,  i.  Tuber  cinereum.  j.  Infundibulum.  k.  Hypophysis.  1.  Cor- 
pus mammillare.  m.  Posterior  perforated  substance,  n.  Ba.sis  pedunculi.  o.  Sulcus 
parclfactorius  anterior.    2  to  i2,  the  cerebral  nerves. 


CONSIDERATIONS    OF   THE    BRAIN    OR    ENCEPHALON.  49 

secretory  fibers  (Pawlow).  The  afferent  or  sensory  fibers  of  the 
vagus  rise  in  the  jugular  and  nodular  ganglia  of  the  nerA'e  {g. 
jugulare  and  g.  nodosum)  within  and  just  below  the  jugular  fora- 
men. Within  the  medulla  are  the  genetic  nuclei  of  the  efferent 
fibers. 

11.  The  accessory  nerve  («.  accessorius)  is  composed  of  a 
cerebral  and  a  spinal  root  both  of  which  are  efferent  in  function 
(Fig.  45).  The  cerebral  root  (radix  cerebralis)  rises  within  the 
medulla  and  issues  from  the  posterior  lateral  sulcus  below  the 
level  of  the  olive  and  immediately  inferior  to  the  roots  of  the 
vagus  {apparent  origin).  This  is  distributed  entirely  by  way  of 
the  vagus.  The  spinal  root  (radix  spinalis),  having  taken  its  ap- 
parent origin  from  the  lateral  surface  of  the  spinal  cord  and 
passed  through  the  foramen  magnum,  joins  the  cerebral  (acces- 
sory)  root  near  the  jugular  foramen. 

12.  Hypoglossal  Nerve.  {N.  hypoglossus). — ^The  twelfth  is 
the  great  motor  nerve  to  the  tongue  (Figs.  21  and  45).  A  half 
dozen  or  more  radicals  make  it  up;  they  rise  in  the  medulla  and 
issue  in  linear  series  from  the  anterior  lateral  sulcus  of  the  medulla 
between  the  pyramid  and  the  olive  {apparent  origin).  The  root 
bundles  which  emerge  from  the  same  sulcus  below  the  level  of 
the  olive  belong  to  the  anterior  root  of  the  first  cer\dcal  nerve. 

The  student  should  now  turn  back  to  Table  I.  Study  it  care- 
fully and  identify  all  the  primary  and  secondary  divisions  of  the 
brain  (Figs.  14,  15,   16,  17,   18,  and  28). 


CHAPTER  III. 
THE  CEREBRUM. 

The  cerebrum  with  its  great  hemispheres  is  that  part  of  the 
brain  which  especially  characterizes  man.  In  man  only  do  the 
hemispheres  reach  such  predominant  development.  Though 
they  are  mere  outgrowths  of  the  anterior  brain-vesicle  in  the 
beginning,  they  completely  overshadow  all  other  parts  of  the 
brain  by  the  seventh  month  of  embryonic  life,  extending  farther 
forward,  backward  and  lateralward  than  any  other  part.  Within 
the  cerebral  hemispheres  lies  the  physical  basis  of  all  mental  func- 
tion; they  constitute  the  central  mechanism  of  thought  and  con- 
sciousness. ■ 

Reference  to  the  table  given  above  shows  that  the  cerebrum 
is  made  up  of  three  parts:  (i)  The  end-brain,  which  includes 
the  cerebral  hemispheres  and  their  connecting  links;  (2)  the 
inter-brain,  comprising  the  thalami  and  their  associated  nuclei, 
which  with  the  former  constituted  the  fore-brain;  and  (3)  the 
mid-brain  (Figs.  17,  18,  and  27).  The  cerebrum  is  an  ovoid 
mass,  flattened  inferiorly,  which  fills  the  vault  of  the  cranium  and 
rests,  below,  upon  the  floor  of  the  cranial  cavity  in  the  anterior 
and  middle  fossas  and  upon  the  tentorium  cerebelli  over  the 
posterior  fossa  (Fig.  2).  Viewed  from  above,  it  is  sufficiently 
round  to  suggest  a  sphere;  and,  being  divided  in  the  median  line 
by  the  longitudinal  fissure,  the  lateral  halves  are  called  hemis- 
pheres. The  most  anterior  point  is  the  frontal  pole,  and  the 
most  posterior  is  the  occipital  pole  (Fig.  22).  In  the  floor  of  the 
longitudinal  fissure  of  the  cerebrum  the  corpus  callosum  can  be 
seen  joining  the  hemispheres  together;  and  beneath  it,  concealed 
from  view,  are  the  fornix  and  anterior  commissure.  Those  are 
the  connecting  links,  proper,  of  the  hemispheres  (Figs.  34,  36  and 
37).  Inferior  to  them  is  found  the  inter-brain.  The  latter  form 
an  additional  union  of  the  hemispheres,  as  may  be  seen  by  viewing 

50 


THE    FORE-BRAIN   OR    PROSENCEPHALON. 


SI 


the  base  of  the  l:)rain.  Just  caudal  to  the  inter-brain  is  the  mid- 
brain which  occupies  the  tentorial  notch  of  the  dura  mater;  and, 
situated  in  the  median  line,  is  so  overhung  by  the  cerebral  hemis- 
pheres as  to  reveal  only  its  anterior  surface.  It  resembles  the 
inter-brain  in  this  respect.  Inferiorly  the  mid-brain  joins  the 
rhombencephalon.     Their  plane  of  union  cuts  the  isthmus  (Fig. 

44)- 

In  studying  the  gross  structures  of  the  cerebrum  it  is  most 
convenient  to  divide  it  into  its  embryologic  divisions,  viz.,  the 
fore-brain  and  the  mid-brain. 

SECTION  I.     THE  FORE-BRAIN  OR  PROSENCEPHALON. 


I.  End-brain 


Fore-brain 


2.  Inter-brain 


Cerebral  Hemispheres  and  their  connecting 

links — 
Corpus  Callosum 
Commissura  Anterior 
Commissura  Hippocampi  (Fornix). 

Thalami 

Mammillary  Bodies  (of  hypothalamus) 
Geniculate  Bodies  (metathalamus) 
Pineal  Body  (of  epithalamus). 


In  order  to  fix  important  landmarks  and  to  learn  the  location 
and  relations  of  the  gross  structures  of  the  fore-brain  it  is  neces- 
sary to  study  in  detail  the  topography  of  the  exterior  surface  and 
the  interior  surface.  It  is  that  vdth  vv^hich  the  present  section 
deals.  For  the  minute  anatomy  of  the  cerebral  structures,  see 
Section  III  of  the  Cerebrum. 


EXTERIOR  SURFACE  OF  FORE-BRAIN. 

The  exterior  surface  of  the  fore-brain  is  composed  of  a  thin 
sheet  of  gray  matter  var)dng  in  thickness  from  one-sixth  to  one- 
quarter  of  an  inch.  That  gray  matter  forms  a  bark-like  cover- 
ing for  the  underlying  wliite  substance  and  is,  therefore,  called 
the  cortex  (Figs.  34  and  35).     It  is  thrown  into  irregular  elongated 


52  THE    CEREBRUM. 

folds  named  convolutions,  or  gyri,  by  deep  linear  depressions, 
which  greatly  increase  the  relative  amount  of  cortical  substance. 
The  hnear  depressions  are  called  fissures,  or  sulci;  and,  in  con- 
sequence of  them,  the  gray  substance  is  increased  in  bulk  to 
fifty-eight  and  one-half  per  cent,  of  the  entire  cerebrum  (DeReg- 
ibus). 

The  name  fissure  is  properly  apphed,  first  to  those  deep  furrows 
which  represent  clefts  between  embryonic  vesicles,  viz.,  the 
median,  verticle  cleft  between  the  cerebral  hemispheres,  and  the 
two  arched  clefts,  one  between  the  cerebellum  and  the  cerebral 
hemispheres  and  the  other  between  the  cerebellum  and  the  poste- 
rior surface  of  the  medulla  oblongata  (Figs.  19  and  20);  and, 
second,  the  deep  linear  depressions  in  the  cerebral  hemisphere 
which  indent  the  entire  ventricular  wall  and  produce  eminences 
on  the  interior  surface  are  properly  called  fissures.  All  other 
furrows  in  the  cerebral  surface  are  called  sulci. 

The  exterior  surface  of  the  fore-brain  is  divided  by  distinct 
borders  into  three  regions,  namely,  the  convex  surface,  the 
medial  surface,  and  the  basal  surface  (Figs.  22,  26  and  27). 
The  basal  surface  comprises  the  orbital  and  tentorial  areas, 
separated  by  the  stem  of  the  fissura  lateralis  cerebri  (Sylvii).  The 
convex  surface  is  separated  from  the  medial  surface  by  the  supero- 
medial  border  {mar go  supero-medialis),  from  the  tentorial  area  of 
the  basal  surface  by  the  infero-lateral  border  {mar go  infer o-lateralis, 
or  in.  occipitalis  lateralis),  and  from  the  orbital  area  of  the  basal 
surface  by  the  superciliary  border  {mar go  superciliaris).  The 
medial  orbital  border  {margo  orbitalis  medialis)  separates  the 
orbital  area  of  the  basal  surface  from  the  medial  surface,  and 
the  medial  occipital  border  {margo  occipitalis  medialis)  divides 
the  medial  surface  from  the  tentorial  area  of  the  basal  surface 
(Figs.  19,  22  and  26). 

FISSURES  AND  SULCI  OF  CONVEX  SURFACE. 

The  convex  surface  of  the  cerebral  hemisphere  {fades  convexa 
cerebri)  is  related  to  two.  very  extensive  fissures,  viz.,  the  longit- 
udinal and  the  transverse.  The  longitudinal  fissure  of  the 
cerebrum  {fissura  longitudinalis  cerebri)  is  the  vertical  median 


FISSURES    AND    SULCI    OF    CONVEX    SURFACE. 


53 


FISSURES    AND    SULCI   OF    CONVEX    SURFACE.  55 

cleft  between  the  hemispheres  of  the  cerebrum  (Figs.  19  and  22). 
It  contains  the  falx  cerebri  (Fig.  i).  Its  floor  is  formed  by  the 
corpus  callosum.  The  cerebrum  is  separated  from  the  cere- 
bellum by  the  transverse  fissure  of  the  cerebrum  (fissura 
transversa  cerebri,  Figs.  20,  27,  i  and  6).  This  fissure  continues 
forward  above  the  mid-brain,  and  terminates  in  the  cerebrum 
between  the  inter-brain  and  the  fornix,  where  it  is  continuous, 
by  its  lateral  extremities,  with  the  chorioidal  fissures  of  the  hem- 
ispheres. The  tentorium  occupies  the  posterior  part.  The 
anterior  part  of  the  transverse  fissure  contains  the  chorioid  tela 
of  the  third  ventricle. 

There  are  three  great  furrows  in  the  convex  surface  of  each 
cerebral  hemisphere  which  form  interlobar  boundaries  and  con- 
stitute very  important  landmarks:  The  fissura  cerebri  lateralis, 
the  sulcus  centrahs,  and  the  sulcus  occipito-parietalis  (Figs.  22 
and  23). 

The  lateral  fissure  {-fissura  cerebri  lateralis,  [Sylvii])  begins 
in  the  fossa  of  the  same  name  at  the  base  of  the  brain  (Fig.  21). 
It  runs  outward  between  the  frontal  and  the  temporal  lobe,  along 
the  lesser  wing  of  the  sphenoid  bone;  and,  turning  upward,  on  the 
convex  surface,  it  divides  three-fourth  inch  behind  the  Sylvian  point 
into  an  anterior  horizontal,  and  anterior  ascending  and  a  posterior 
ramus  (Fig.  23).  Into  the  frontal  lobe  project  the  small  anterior 
rami.  They  are  separated  by  the  foot  (posterior  end)  of  the  inferior 
frontal  gyrus,  called  the  pars  triangularis.  Below  the  anterior 
horizontal  ramus  is  a  knuckle  of  the  same  frontal  gyrus  which 
forms  the  pars  orbitalis;  and,  between  the  ascending  and  posterior 
rami,  is  located  the  pars  opercularis,  constituting  the  connecting 
gyrus  between  the  anterior  and  posterior  central  gyri.  The 
inferior  frontal  gyrus  forms  the  frontal  part  of  the  operculum 
(pars  frontalis  operculi).  The  operculum  (operculum,  a  cover) 
covers  the  island.  The  posterior  limb  of  the  lateral  cerebral 
fissure  separates  the  temporal  lobe  from  the  parietal.  Near 
the  crotch  and  within  the  fissure  is  situated  the  island.  A  fine 
drawn  from  the  Sylvian  point,  one  and  one-quarter  inches  be- 
hind the  zygomatic  process  of  the  frontal  bone  and  one  and  a  half 
inches  above  that  of  the  temporal,  backward  to  the  subparietal 


56  THE    CEREBRUM. 

point,  three-quarters  of  an  inch  below  the  tuber  parietale,  lies 
directly  over  the  posterior  ramus  of  this  fissure. 

The  Sulcus  Centralis  (Rolandi,  Figs.  22,  23,  24  and  27). — 
Beginning  just  above  the  posterior  limb  of  the  lateral  cerebral 
fissure,  is  the  central  sulcus,  which  extends  upward  and  backward 
to  the  longitudinal  fissure  of  the  cerebrum.  Its  upper  extremity 
is  about  half  an  inch  (or  5.7  per  cent.)  behind  the  middle  of  a 
fine  dra^^-n  from  the  nasal  eminence  to  the  external  occipital 
protuberance.  With  this  sagittal  meridian  the  sulcus  centrahs 
forms  an  anterior  angle  of  69  to  74  degrees.  The  average  Rolandic 
angle  is  71°  7'  (Cunningham).  The  sulcus  centrahs  is  three 
and  three-eighths  inches  long  and  forms  the  boundar}^  between 
the  frontal  and  the  parietal  lobe.  It  is  developed  in  two  parts 
a  superior  third  and  an  inferior  two-thirds,  which  join  at  an  angle 
open  backward,  caUed  the  genu  superius ;  both  parts  may  present 
an  anterior  conca\dty.  Often  a  concealed  gyrus  separates  the 
two  parts  of  the  sulcus  at  the  genu  superius  (Fig.  22).  This 
superior  genu  is  in  Hne  "with  the  superior  frontal  sulcus  and  marks 
the  probable  location  of  the  trunk  center  and  the  boundary  between 
the  arm  and  leg  areas  in  the  anterior  central  g}'rus.  There  is  a 
less  constant  angle,  the  genu  inferius,  in  the  lower  part  of  the 
central  sulcus;  it  is  in  hne  mth  the  inferior  frontal  sulcus  and 
marks  the  lower  Hmit  of  the  arm  area  and  the  upper  hmit  of  the 
face  area. 

The  Occipito-parietal  Sulcus.  (Sulcus  occipito-parietalis). — 
If  the  hne  on  the  skuU  locating  the  posterior  limb  of  the  lateral 
cerebral  fissure  be  extended  back  to  the  sagittal  meridian  its 
posterior  end  marks  the  location  of  the  occipito-parietal  sulcus. 
The  sulcus  is  located  one- sixth  of  an  inch  above  the  lambda  in 
the  adult,  and  is  from  one  and  a  hah  to  two  inches  above  the 
occipital  pole.  The  greater  part  of  the  occipito-parietal  sulcus 
is  situated  on  the  medial  surface  of  the  cerebral  hemisphere,  hence, 
it  is  divided  into  an  internal  part  and  an  external  part  which  are 
continuous  through  the  supero-medial  border  (Figs.  20,  22  and  28). 
To  the  extent  of  its  depth,  which  is  about  one  inch,  the  external 
occipito-parietal  sulcus  separates  the  occipital  from  the  parietal 
lobe  on  the  convex  surface   of  the  hemisphere.     Cunningham 


FISSURES    AND    SULCI    OF    CONVEX    SURFACE. 


57- 


LOBES  AND  GYRI  OF  THE  CONVEX  SURFACE.        59 

considers  the  occipito-parietal  sulcus  a  true  Fissure  because  in  the 
embryo  it  produces  a  ventricular  eminence,  though  it  disappears 
during  development.* 

LOBES  AND  GYRI  OF  THE  CONVEX  SURFACE. 

(1)  The  frontal  lobe  (lobus  frontalis)  comprises  the  anterior 
polar  region  of  the  hemisphere  and  forms  a  part  of  all  three  sur- 
faces (Figs.  22,  28  and  26).  On  the  convex  surface,  it  extends 
as  far  back  as  the  central  sulcus  and  the  lateral  cerebral  fissure; 
on  the  basal  surface,  it  is  bounded  behind  by  the  stem  of  the 
lateral  cerebral  fissure  and  the  anterior  perforated  spot;  and  it  is 
limited  posteriorly  by  the  sulcus  cinguli  on  the  medial  surface 
of  the  cerebral  hemisphere. 

On  the  convex  surface,  the  frontal  lobe  has  the  following  stilci 
and  gyri  (Figs.  23  and  24): 

Superior  precentral  (s.  praecentralis  superior) 
Inferior  precentral  (s.  praecentralis  inferior) 
Superior  frontal  (s.  frontalis  superior) 
Inferior  frontal  (s.  frontalis  inferior) 
Middle  frontal  (s.  frontalis  medius) 
Paramedial  (s.  paramedialis). 

f  Anterior  central  (g.  centralis  anterior) 
•  J  Superior  frontal  (g.  frontalis  superior) 
■^      I  Middle  frontal  (g.  frontalis  medius) 
[  Inferior  frontal  (g.  frontalis  inferior). 

The  precentral  sulci  (Fig.  23)  are  parallel  with  the  central 
sulcus  and  are  located  about  a  half  inch  in  front  of  it,  the  lower 
end  of  the  inferior  precentral  being  insinuated  between  the  central 
sulcus  and  the  ascending  ramus  of  the  lateral  fissure  of  the  cere- 
brum. They  form  the  anterior  boundary  of  the  anterior  central 
gyrus.  The  superior  frontal  sulcus  and  the  inferior  frontal  sulcus 
are  respectively  continuous  with  the  corresponding  precentral 
sulcus  from  which  they  trend  do\Miward  and  forward  parallel 

*The  name  of  this  sulcus  is  written  "occipito-parietal"  rather  than 
"  parieto-occipital;"  this  is  a  simpler  word  to  pronounce  as  it  avoids 
having  "oocc"  in  the  middle  of  it. 


Sulci 


6o  THE    CEREBRUM. 

with  the  supero-medial  border  of  the  hemisphere.  They  separate 
from  each  other  three  gyri  of  nearly  equal  width,  viz.,  the  superior, 
middl^e  and  inferior  frontal  gyri  (Fig.  24). 

The  superior  frontal  gyrus  is  incompletely  divided  in  the 
human  brain  by  an  interrupted  sulcus,  called  the  sulcus  para- 
medians (Fig.  23)  which  is  located  near  the  supero-medial  border 
of  the  hemisphere  and  is  said  by  Cunningham  to  be  better  developed 
in  the  higher  types  of  the  human  race  and  to  be  rare  in  the  higher 
apes. 

A  series  of  shallow  furrows,  described  by  Eberstaller  as  the 
middle  frontal  sulcus  (s.  frontalis  medius,  Fig.  23)  partially  sub- 
divides the  middle  frontal  gyrus  into  an  upper  and  a  lower  part. 
The  middle  frontal  sulcus,  not  found  below  the  anthropoid  apes 
(Cynningham),  is  best  marked  anteriorly  and,  at  the  superciliary 
border  of  the  hemisphere,  bifurcates  and  forms  a  horizontal 
furrow,  the  fr  onto -mar  ginal  sulcus.  The  posterior  end,  the 
foot,  of  the  middle  frontal  gyrus,  hke  that  of  the  superior  and 
inferior  frontal,  lies  in  the  psychic-motor  zone  of  the  brain.  It 
contains  the  writing  center  (Gordinier)  in  the  left  hemisphere 
of  right-handed  people. 

The  inferior  frontal  gyrus  is  highly  developed  in  the  human 
brain,  especially  in  the  left  hemisphere  of  right-handed  people. 
It  is  deeply  cleft  along  its  lower  border  by  the  anterior  ascending 
and  anterior  horizontal  rami  of  the  lateral  fissure  of  the  cerebrum 
and  is  thus  divided  into  a  pars  orbitalis,  situated  below  the  anterior 
horizontal  ramus,  a  pars  triangularis,  inclosed  between  the  ante- 
rior horizontal  and  ascending  rami,  and  a  pars  basilaris,  located 
between  the  anterior  ascending  ramus  of  the  lateral  fissure  and 
the  inferior  precentral  sulcus.  The  pars  basilaris  constitutes  the 
foot  of  the  inferior  frontal  gyrus  and  is  continuous  with  the  gyrus 
centralis  anterior;  on  the  left  side  it  contains  the  speech  center. 
The  anterior  portions  of  the  superior  middle  and  inferior  frontal 
gyri  comprise  a  psychic  center,  center  of  attention,  volition,  in- 
hibition, etc.,  "of  abstract  concept"  (Mills). 

The  anterior  central  gyrus  {g.  centralis  anterior)  lies  between 
the  precentral  sulci  and  the  central  sulcus.  It  is  joined  to  the 
posterior    central    gyrus  by   the   paracentral  lobule,    above  the 


LOBES  AND  GYRI  OF  THE  CONVEX  SURFACE. 


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LOBES  AND  GYRI  OF  THE  CONVEX  SURFACE. 


63 


central  sulcus,  and  by  the  fronto-parietal  part  of  the  operculum, 
below  it.  The  anterior  central  gyrus,  together  with  the  para- 
central lobule  constitutes  the  emissive  motor  zone  of  the  human 
cerebrum. 

(2)  The  parietal  lobe  {lohus  parietalis)  is  situated  behind 
the  central  sulcus  and  above  the  posterior  limb  of  the  lateral 
fissure  of  the  cerebrum  (Figs.  22  and  28).  From  the  curve  near 
the  posterior  end  of  the  latter  to  the  occipito-parietal  sulcus  the 
lobe  is  separated  from  the  temporal,  below,  and  the  occipital, 
behind,  by  an  imaginary  line.  This  imaginary  line  runs  back- 
ward parallel  with  the  infero-lateral  border  of  the  hemisphere 
to  the  boundary  of  the  occipital  lobe;  and  then,  obliquely  upward 
toward  the  supero-medial  border  in  a  line  drawn  from  the  pre- 
occipital notch  to  the  occipito-parietal  sulcus.  Extending  over 
the  supero-medial  border,  the  lobe  on  the  medial  surface  is  inclosed 
between  the  occipito-parietal  sulcus  behind  and  the  marginal 
part  of  the  sulcus  cinguli  in  front,  and  is  bounded  antero-inferiorly 
by  the  subparietal  sulcus. 

On  the  convex  surface  of  the  hemisphere  the  parietal  lobe 
possesses  the  following  sulci  and  gyri  (Figs.  23  and  24). 

Interparietal  (s.  interparietalis)  four  parts — 
Inferior  post -central  (s.  post-centralis  inferior; 
Superior  post -central  (s.  post-centralis  superior) 
Horizontal  limb  (ramus  horizontalis) 
Occipital  limb  (ramus  occipitalis). 


Sulci 


Gyri 


Upturned  ends  of 

Lateral  fissure  (f.  cerebri  lateralis) 

Superior  temporal  sulcus  (s.  temporalis  superior) 

Middle  temporal  sulcus  (s.  temporalis  medius). 

Posterior  central  (g.  centralis  posterior) 
Superior  parietal  lobule  (1.  parietalis  superior) 
Inferior  parietal  lobule  (1.  parietalis  inferior) 

Supramarginal  (g.  supramarginalis) 

Angular  (g.  angularis) 

Postparietal  (g.  postparietalis). 


The' '  interparietal   sulcus  (Figs.  20  and  23)  is  the  only  one 
belonging  to  the  parietal  lobe.     The  inferior  and  superior  post- 


64  THE    CEREBRUM. 

central  sulci,  constituting  its  anterior  parts,  are  parallel  with  the 
central  sulcus  and  are  located  a  half  or  three-quarters  of  an  inch 
behind  it,  separated  from  the  central  sulcus  by  the  gyrus  centralis 
posterior.  The  post-central  sulci  are  often  not  continuous.  The 
inferior  is  about  twice  the  length  of  the  superior,  in  this  resembling 
the  central  sulcus,  and  usually  it  is  joined  at  its  upper  end  to  the 
horizontal  limb  of  the  interparietal  sulcus.  The  horizontal  part 
of  the  sulcus  lies  about  an  inch  below  the  supero-medial  border 
of  the  hemisphere  with  which  it  is  parallel ;  it  separates  the  superior 
parietal  lobule  from  the  inferior  parietal  lobule  and  is  continued 
as  ramus  occipitalis  into  the  occipital  lobe  where  it  bifurcates. 

The  posterior  central  gyrus  reaches  from  the  posterior  limb 
of  the  lateral  fissure  upward  and  backward,  between  the  central 
and  post-central  sulci,  to  the  longitudinal  fissure  of  the  cerebrum 
(Fig.  24).  It  is  joined  to  the  anterior-central  gyrus  around  the 
ends  of  the  central  sulcus  by  superficial  annectant  gyri  (gyri 
transitivi)  and  sometimes  is  connected  with  it  by  a  buried  gyrus 
(g.  profundus  transitivus)  wliich,  deeply,  separates  the  superior 
from  the  inferior  part  of  the  central  sulcus.  The  annectant 
gyrus  which  closes  the  central  sulcus  superiorly  and  hnks  together 
the  central  gyri  is  the  paracentral  lobule  (lobulus  paracentralis) ; 
the  fronto-parietal  part  of  the  operculum  joins  them  below  the 
central  sulcus.  The  posterior  central  gyrus  and  paracentral 
lobule  constitute  the  receptive  area  of  common  sensation,  the 
somcEstketic  area,  so  far  as  it  extends  on  the  convex  surface. 

The  superior  parietal  lobule  (Figs.  20  and  24)  forms  the 
supero-medial  border  of  the  hemisphere  from  the  superior  post- 
central to  the  occipito-parietal  sulcus.  It  is  separated  from  the 
inferior  parietal  lobule  by  the  horizontal  part  of  the  interparietal 
sulcus;  posteriorly,  it  is  joined  to  the  occipital  lobe  by  a  curved 
annectant  gyrus,  called  the  arcus  occipito-parietalis,  which  closes 
the  superior  end  of  the  occipito-parietal  sulcus;  and,  over  the 
supero-medial  border,  it  is  continuous  with  the  praecuneus  of  the 
medial  surface.  In  the  prascuneus  and  the  superior  parietal 
lobule  Mills  locates  the  stereo  gnostic  center  (Figs.  56  and  57). 

The  Inferior  Parietal  Lobule.— The  inferior  parietal  lobule 
is  incompletely  divided  into  two  or  three  gyri.     Named  from 


LOBES  AND  GYRI  OF  THE  CONVEX  SURFACE. 


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LOBES  AND  GYRI  OF  THE  CONVEX  SURFACE.        67 

before  backward  they  are  as  follows:  The  supramarginal,  the 
angular  and  the  post-parietal  (Figs.  20  and  24). 

The  supramarginal  gyrus  arches  over  and  closes  the  upturned 
end  of  the  posterior  ramus  of  the  lateral  fissure  of  the  cerebrum 
(Fig.  24).  The  anterior  segment  of  the  arch  is  continuous  with 
the  posterior  central  gyrus  and  is  comprised  in  the  psychic-sensory 
area;  the  posterior  segment  of  the  arch  fuses  with  the  angular 
gyrus,  behind,  and  the  superior  temporal  gyrus,  below,  and 
belongs  to  the  psychic-sensory  area,  also,  the  motor  memory  center 
(Fig.  56). 

The  angular  gyrus  forms  an  arch  oxer  the  end  of  the  superior 
temporal  sulcus  (Figs.  20  and  24).  The  angular  arch  is  in  direct 
continuity  with  the  superior  and  middle  temporal  g}'ri  and  the 
posterior  segment  of  it  is  continuous  with  the  post-parietal  gyrus 
when  that  gyrus  is  present. 

The  post-parietal  gyrus  is  present  onh-  when  the  middle 
temporal  sulcus  bends  upward  and  terminates  in  the  parietal 
lobe;  in  w^hich  case  this  gyrus  curves  over  and  closes  that  sulcus 
(not  figured).  It  connects  the  posterior  ends  of  the  inferior  and 
middle  temporal  gyri  and  also  blends  ^^ith  the  superior  occipital 
g}Tus.  The  angular,  post-parietal  and  superior  occipital  g}'ri  on 
the  left  side,  according  to  Mills  and  others,  constitute  the  center 
for  visual  memories.  The  studies  of  A.  W.  Campbell  render  it 
probable  that  the  visual  cortex  does  not  extend  into  the  parietal 
lobe  of  man  at  all.  The  receptive  \isual  center  for  macular  vision 
(vision  in  the  macula  lutea  of  the  retina)  is  likewise  located  in 
the  angular  or  post-parietal  g}''rus  by  Mills,  but  it  is  probably 
situated  on  the  medial  surface  of  the  occipital  lobe;  unlike  the 
memory  center,  this  is  present  in  both  hemispheres. 

(3)  Occipital  Lobe.  {Lobus  occipitalis,  Figs.  20,  22,  24,  26 
and  28). — The  occipital  lobe  forms  the  posterior  pole  of  the  hem- 
isphere. With  the  parietal  and  temporal  lobes  it  is  directly  con- 
tinuous, being  marked  off  from  them  by  an  imaginary  line  drawn 
from  the  preoccipital  notch  to  the  occipito-parietal  sulcus.  This 
sulcus,  on  the  convex  surface,  bounds  it  to  the  extent  of  about 
an  inch;  rarely,  the  external  perpendicular  sulcus  bounds  it  in 
front.     On  the  medial  and  basal  surfaces  of  the  hemisphere  the 


68  THE    CEREBRUM. 

occipital  lobe  extends  from  the  occipito-parietal  sulcus  to  the  pre- 
occipital notch,  and  is  separated  from  the  temporal  lobe  on  the 
basal  surface  by  an  imaginary  line  drawn  from  this  notch  toward 
the  posterior  end  of  the  corpus  callosum,  to  the  isthmus  of  the 
limbic  lobe.  The  occipital  lobe  has  the  form  of  a  triangular 
pyramid  whose  borders  are  the  supero-medial,  the  infero-lateral 
and  the  medial  occipital  borders  of  the  cerebral  hemisphere. 
Those  borders  meet  at  its  apex,  the  occipital  pole. 

The  occipital  lobe  is  somewhat  rudimentary  in  man,  though 
present  only  in  apes  and  men  (Cunningham).  It  makes  its  ap- 
pearance at  the  fourth  month  in  utero,  and  is  distinctly  outHned  by 
fissures  on  all  three  surfaces  at  the  sixth  month,  when  it  resembles 
the  same  lobe  in  the  adult  ape's  brain  (Cunningham  Memoirs). 
After  the  sixth  month  the  fissural  boundaries  largely  disappear 
from  the  human  brain  on  the  convex  and  basal  surfaces;  hence, 
the  artificial  boundaries  in  the  adult.  Its  rudimentary  character 
probably  accounts  for  the  great  variability  in  the  sulci  and  gyri 
of  the  occipital  lobe.  On  the  convex  surface  they  are  usually 
as  follows: 

{Ramus  occipitalis  of  interparietal  sulcus. 
Transverse  occipital  (s.  occipitalis  transversus) 
Lateral  occipital  (ss.  occipitales  laterales). 

.  I  Superior  occipital  (gg.  occipitales  superiores) 
•^      I  Lateral  occipital  (gg.  occipitales  laterales). 

The  lateral  occipital  sulcus  is  the  only  one  properly  belonging 
to  the  convex  surface  of  the  occipital  lobe  (sometimes  there  are 
two  of  them).  It  divides  that  surface  almost  equally  into  a 
superior  and  lateral  gyrus,  both  of  which  may  be  double.  The 
sulcus  begins  near  the  supero-medial  border.  It  follows  a  merid- 
ian which  is  nearly  parallel  with  the  infero-lateral  border  of 
the  lobe  and  runs  forward,  often  presenting  one  interruption, 
to  the  occipito-temporal  boundary  line  where  is  bifurcates  and 
forms  a  short  perpendicular  sulcus,  which  represents  the  affens- 
palte  of  the  ape  (ElUot  Smith).  When  the  lateral  occipital  sulcus 
is  double  there  are  two  lateral  gyri  (Figs.  20,  23  and  24). 

The   occipital   limb   of    the   interparietal  sulcus  descends  in 


LOBES  AND  GYRI  OF  THE  CONVEX  SURFACE.        69 

the  occipital  lobe  a  variable  distance  (Fig.  20).  It  is  not  always 
continuous  with  the  horizontal  limb.  Running  about  an  inch 
from  the  supero-medial  border  of  the  hemisphere,  it  passes  the 
occipito-parietal  sulcus,  from  which  it  is  separated  by  the  arcus 
occipiio-parietalis,  and  bifurcates  in  the  superior  occipital  gyrus 
into  two  more  or  less  oblique  branches,  constituting  the  trans- 
verse occipital  sulcus.  The  medial  end  of  the  transverse  sulcus 
may  or  may  not  cut  the  supero-medial  border  of  the  lobe. 

The  lateral  occipital  gyrus  (Figs.  20  and  24)  lies  below  the 
lateral  occipital  sulcus  and  extends  from  the  occipital  pole  forward 
along  the  infero-lateral  border  of  the  hemisphere  to  the  preoccip- 
ital notch.  Sometimes  it  is  di\ided  into  two  lateral  gv'ri  by  an 
inferior  lateral  sulcus.  It  is  continuous  with  the  inferior  tem- 
poral gyrus,  except  rarely,  when  the  two  are  separated  by  the 
external  perpendicular  sulcus. 

The  superior  occipital  gyrus  forms  the  upper  half  of  the 
convex  surface  of  the  lobe  (Figs.  20  and  24).  It  is  incompletely 
separated  from  the  lateral  occipital  gyrus  by  the  lateral  occipital 
sulcus  and  is  often  divided  into  two  gyri.  It  is  continuous  ^rith 
the  post-parietal  g}Tus  around  the  lateral  end  of  the  transverse 
occipital  sulcus;  and,  around  the  medial  end  of  that  sulcus,  it 
is  joined  to  the  superior  parietal  lobule  by  the  arcus  occipiio- 
parietalis.  The  latter  is  a  sharply  curved  annectant  g}^rus  which 
bounds  the  occipito-parietal  sulcus.  When  the  middle  temporal 
sulcus  does  not  turn  upward  at  its  posterior  end  and  temiinate 
in  the  parietal  lobe,  the  superior  occipital  gyrus  is  continuous 
in  front  with  the  middle  temporal  and  angular  gyri.  As  already 
mentioned,  the  superior  occipital  g}'rus,  according  to  ^liUs, 
belongs  to  the  center  for  visual  memories. 

(4)  The  temporal  lobe  {lobus  temporalis,  Figs.  20,  22,  23,  24, 
25  and  26)  is  that  part  of  the  cerebral  hemisphere  behind  the 
main  stem  and  below  the  posterior  Umb  of  the  lateral  cerebral 
fissure.  It  rests  in  the  middle  fossa  of  the  skull;  forms  the 
temporal  pole  of  the  hemisphere;  and  is  continuous  posteriorly 
with  the  occipital  and  parietal  lobes,  from  which  it  is  marked 
off  only  by  the  imaginary  lines  already  described.  On  the  basal 
surface  of  the  hemisphere,  the  temporal  lobe  along  its  medial 


70  THE    CEREBRUM. 

border  is  separated  from  the  limbic  lobe  by  the  collateral  fissure 
and  by  a  short  furrow,  which  is  shallow  in  the  adult  human  brain, 
called  the  sulcus  ecto-rhinalis.  The  temporal  lobe  is  attached 
to  the  hemisphere  posteriorly  and  medially;  but  it  presents  three 
free  surfaces — a  superior,  an  external  and  an  inferior — which  meet 
at  the  anterior  point,  called  the  temporal  pole. 

The  superior  surface  of  the  temporal  lobe  forms  the  inferior 
wall  of  the  lateral  cerebral  fissure  (Fig.  25).  It  looks  somewhat 
medianward  toward  the  island  and  constitutes  the  temporal  part 
of  the  operculum.  It  is  separated  from  the  island  by  the  inferior 
circular  sulcus  {s.  circularis  insula).  Anteriorly,  the  superior 
surface  of  the  temporal  lobe  is  smooth;  posteriorly,  it  possesses 
one  or  two  shallow  transverse  temporal  sulci  which  feebly  outline 
two  or  three  gyri,  called  the  transverse  temporal  gyri  of  Heschl 
(gyri  tern por ales  transversi).  These  transverse  gyri  belong  to 
the  receptive  auditory  center  (Figs.  31,  35,  36  and  54). 

The  external  surface  of  the  temporal  lobe  presents  the  fol- 
lowing sulci  and  gyri  (Figs.  23  and  24): 


Sulci  - 


Superior  temporal  (s.  temporalis  superior) 
Middle  temporal  (s.  temporalis  medius) 
Inferior  temporal  (s.  temporalis  inferior).     This  is 
really  on  the  inferior  surface  of  the  lobe. 


r  Superior  temporal  (g.  temporalis  superior) 
Gyri  I   Middle  temporal  (g.  temporalis  medius) 
[  Inferior  temporal  (g.  temporalis  inferior). 

The  superior  temporal  and  middle  temporal  sulci  (Fig.  23)  di- 
vide the  external  surface  into  three  nearly  equal  gyri;  they  run 
parallel  with  each  other,  with  the  infero-lateral  border  and  with 
the  lateral  cerebral  fissure.  The  superior  temporal  sulcus,  like 
the  lateral  fissure,  bends  upward  at  its  posterior  extremity;  it 
terminates  in  the  concavity  of  the  angular  gyrus.  The  middle 
temporal  sulcus  is  usually  an  interrupted  one.  It  may  present 
an  upward  curve  at  its  posterior  end  which  is  bounded  and  closed 
by  the  post-parietal  gyrus ;  or  it  may  continue  in  its  original  direc- 
tion toward  the  occipital  lobe. 

The  inferior  temporal  sulcus,  situated  in  the  tentorial  area  of 


LOBES  AND  GYRI  OF  THE  CONVEX  SURFACE.        7 1 

the  basal  surface,  runs  interruptedly  dose  to  the  infero-lateral 
border  of  the  hemisphere  and  parallel  with  it  (Fig.  26).  It  sep- 
arates the  inferior  temporal  gyrus  from  the  fusiform  gyrus. 

The  superior  temporal,  the  middle  temporal  and  the  inferior 
temporal  gyri  are  of  nearly  equal  width  (Figs.  24  and  26).  They 
fuse  with  one  another  and  with  the  fusiform  gyrus  at  the  temporal 
pole.  The  superior  temporal  gyrus  is  continuous  with  the  supjra- 
marginal  and  angular  gyri,  posteriorly:  in  its  third  and  fourth 
fifths  and  in  the  transverse  temporal  gyn  is  the  receptive  auditory 
center  (Barker). 

The  middle  temporal  gyrus  fuses  at  its  posterior  end  with 
the  angular  gyrus  and  either  with  the  post-parietal  or  the  superior 
occipital.  Along  the  superior  temporal  sulcus,  in  the  middle 
two-fourths  of  the  superior  and  middle  temporal  g\'ri  is  the  center 
for  auditory  m.emories,  the  psychic  auditory  center.  This  center 
is  in  the  left  hemisphere  of  right  handed  people  (Figs.  54  and  56). 

The  inferior  temporal  gyrus  forms  the  infero-lateral  border 
of  the  hemisphere  (Figs.  24  and  26).  It  is  continuous  with  the 
lateral  occipital  gyrus  and  sometimes,  also,  with  the  superior 
occipital  and  post-parietal  gyn..  If  this  gyrus  and  the  lower 
half  of  the  middle  temporal  gyrus  be  di\dded  into  four  equal  parts, 
each  fourth,  according  to  Mills,  belongs  to  a  definite  center. 
From  behind  forward  they  are  the  center  of  orientation;  the  center 
of  equilibration  {?);  the  naming  center;  and,  in  the  anterior  fourth 
and  the  pole  of  the  temporal  lobe,  the  center  of  intonation  (Fig.  56). 

(5)  The  island  {insula,  Reili)  is  also  called  the  central  lobe 
(Figs.  25,  26,  31  and  36).  It  is  situated  in  the  medial  wall  of 
the  lateral  fissure  of  the  cerebrum,  between  the  frontal,  parietal 
and  temporal  lobes,  whose  growth,  after  the  fifth  month  in  utero, 
gradually  covers  it  over.  At  the  end  of  the  first  year  of  extrauterine 
life  it  is  entirely  concealed  by  temporal,  parietal,  and  frontal 
parts  of  the  operculum.  The  island  is  thus  separated  from  the 
general  surface  of  the  cerebral  hemisphere  by  a  distance  of  half 
or  three-quarters  of  an  inch.  It  is  triangular  in  shape.  Its 
apex  is  directed  do\\Tiward  and  forward  toward  the  fossa  lateralis 
cerebri,  and  is  called  the  pole  (polus  insulcE).  If  the  lips  of  the 
lateral  fissure  be  widely  separated,  the  sulcus  circularis  insulae 


72  THE    CEREBRUM. 

may  be  seen  separating  the  island  from  the  frontal,  parietal  and 
temporal  lobes  (Figs.  25,  26  and  36).  The  circular  sulcus  is 
lacking  only  at  the  antero-inferior  part,  at  the  pole,  where  the 
cortex  of  the  island  is  continuous  with  that  of  the  posterior  orbital 
gyrus  and  with  the  anterior  perforated  substance,  and  is  on  the 
same  level  as  the  orbital  area  of  the  basal  surface.  The  imaginary 
line  separating  the  anterior  perforated  substance  from  the  island 
is  called  the  threshold  of  the  island  (limen  insula). 

In  the  island  there  is  one  named  sulcus  and  jour  to  six  gyri 
which  have  a  radial  or  fan-like  grouping  (Fig.  25): 

Sulcus  \   Central  of  the  island  (s.  centralis  insulae). 

.  j  Short  (gyri  breves),  three  or  four  of  them. 
^     \  Long  (gyrus  longus — furcahs). 

The  sulcus  centralis  insula  begins  at  the  apex,  or  pole,  of  the 
island  and  runs  obliquely  upward  and  backward  dividing  the 
lobe  into  two  lobules  (Fig.  25).  It  is  in  the  same  transverse  plane 
as  the  central  sulcus  (of  Rolando).  In  front  of  it,  is  the  pre- 
central  lobule  composed  of  the  short  gyri  and  continuous  with 
the  frontal  lobe;  the  post-central  lobule  hes  behind  it  and  is  in 
continuity  with  the  parietal,  temporal  and  limbic  lobes. 

The  gyri  breves  insulae,  three  or  four  in  number,  are  separated 
by  shallow  furrows  which  diverge  upward  and  backward  from 
the  smooth  apex  of  the  precentral  lobule  (Fig.  25).  They  are 
joined  to  the  orbital  operculum  by  a  short  annectant  gyrus  {gyrus 
transversus  insula  of  Eherstaller)  which  extends  from  the  apex 
around  the  lower  end  of  the  anterior  circular  sulcus.  Their 
connection  under  the  circular  sulcus  with  the  foot  of  the  inferior 
frontal  gyrus  suggests  a  participation  in  the  speech  center,  and 
they  are  figured  by  Mills  in  that  center.  However,  the  paraphasia 
which  results  from  lesions  in  the  short  gyri  may  be  due  to  the 
involvement  of  an  association  tract  of  fibers  running  underneath 
them. 

Gyrus  Longus  (Furcalis)  (Fig.  25). — ^It  Hes  behind  the  central 
sulcus  of  the  island  and  trends  obliquely  backward  and  upward. 
Posteriorly,  it  bifurcates  for  a  short  distance  forming  two  short 
branches  which  are  continuous  under  the  circular  sulcus  with  the 


THE    BASE    OF   THE    FORE-BRAIN.  73 

parietal  lobe;  it  fuses  mth  the  temporal  lobe  and  the  gyrus  hippo- 
campi of  the  limbic  lobe,  inferioriy. 

The  oljactory  lobe  and  the  limbic  lobe,  comprising  the  rhinen- 
cephalon  and  a  part  of  the  neopallium,  also  belong  to  the  cerebral 
hemisphere;  but  no  part  of  either  can  be  seen  on  the  convex  sur- 
face (Figs.  28,  21  and  i8). 

THE  BASE  OF  THE  FORE-BRAIN. 

The  basal  or  inferior  surface  of  the  fore-brain  comprises  the 
inferior  surface,  first,  of  the  end-brain,  including  the  pars  optica 
hypothalami  and  the  cerebral  hemispheres;  and,  second,  of  the 
inter-brain,  which  embraces  the  pars  mammillaris  hypothalami. 
It  is  completely  exposed  only  when  a  section  is  made  through  the 
mid-brain  and  the  rhombencephalon  removed  (Figs.  21  and  26). 
This  should  now  be  done  ^^ith  a  thin,  moistened  brain-knife. 
Make  the  section  from  before  backward  and  upward,  at  a  right 
angle  to  the  axis  of  the  mid-brain.  Now  notice,  first,  the  section 
of  the  mid-brain  and,  just  anterior  to  that,  the  median  structures 
of  the  fore-brain,  occup}dng  the  center  of  the  field;  and,  second, 
the  surrounding  inferior  surface  of  the  cerebral  hemispheres. 
The  latter  form  the  very  large  peripheral  zone. 

The  base  of  the  cerebral  hemisphere  extends  from  the  frontal 
to  the  occipital  pole.  In  front  it  is  composed  of  the  orbital  area 
bounded  by  the  medial  orbital  and  superciHary  borders;  and,  pos- 
teriorly, is  made  up  of  the  tentorial  area,  which  is  bounded,  later- 
ally, by  the  infero-lateral  border,  and,  medially,  by  the  chorioidal 
fissure  and  the  medial  occipital  margin  of  the  hemisphere  (Fig. 
26).  The  orbital  area  embraces  the  inferior  surface  of  the  frontal 
lobe  and  of  the  island,  and  the  whole  olfactory  lobe;  while  the 
inferior  surface  of  the  temporal  and  occipital  lobes,  and  the  g}Tus 
hippocampi  and  fascia  dentata  of  the  limbic  lobe  are  included  in 
the  tentorial  area. 

Frontal  Lobe,  Inferior  Surface  (Fig.  26). — ^The  inferior  surface 
of  the  frontal  lobe,  resting  on  the  orbital  plate  of  the  frontal  bone, 
is  often  called  the  orbital  lobe.  It  is  separated  from  its  fellow 
bv  the  longitudinal  fissure  of  the  cerebrum,  and  is  bounded  behind 


74  THE    CEREBRUM. 

by  the  lateral  fossa  and  lateral  fissure  of  the  cerebrum,  overlapped 
by  the  temporal  lobe.  More  accurately,  the  posterior  boundary 
is  the  anterior  perforated  substance  and  the  anterior  part  of  the 
circular  sulcus.  The  orbital  lobe  is  concave  transversely  and 
is  divided  by  the  triradiate  or  H-shaped  sulcus  orbitalis,  made 
up  of  the  medial  orbital,  the  transverse  orbital  and  the  lateral  orbital 
sulci;  and  by  the  olfactory  sulcus,  which  is  close  to  the  longitud- 
inal fissure  and  parallel  with  it.     Five  gyri  are  thus  formed : 


Gyri 


Straight  (g.  rectus) 

Medial  orbital  (g.  orbitalis  medialis) 

Lateral  orbital  (g.  orbitalis  lateralis),  not  constant 

Anterior  orbital  (g.  orbitalis  anterior) 

Posterior  orbital  (g.  orbitalis  posterior). 


The  gyrus  rectus  (Fig.  26)  forms  the  medial  border  of  this 
surface.  It  is  separated  from  the  medial  orbital  gyrus  by  the 
sulcus  olfactorius  in  which  lie  the  olfactory  bulb  and  tract.  Over 
on  the  medial  surface  it  forms  a  part  of  the  marginal  gyrus  and 
it  joins  the  superior  frontal  at  the  frontal  pole.  Posteriorly,  the 
gyrus  rectus  is  separated  from  the  parolfactory  area  (of  Broca) 
by  a  slight  furrow,  the  anterior  parolfactory  sulcus. 

The  medial  orbital  gyrus  lies  between  the  sulcus  of  the  same 
name  and  the  sulcus  olfactorius  (Fig.  26).  It  extends  from  the 
frontal  pole  to  the  anterior  perforated  substance  and  the  island. 
The  anterior  and  posterior  orbital  gyri  He  within  the  H-shaped 
orbital  sulcus  separated  from  each  other  by  the  transverse  orbital 
sulcus.  The  former  is  continuous  with  the  frontal  gyri  at  the 
superciliary  border;  the  latter  is  only  partially  separated,  behind, 
from  the  island  by  the  anterior  circular  sulcus ;  the  posterior  orbital 
gyrus  is  likewise  continuous  with  the  posterior  end  of  the  lateral 
orbital  gyrus  and  with  the  orbital  portion  of  the  inferior  frontal. 
The  lateral  orbital  gyrus,  which  is  a  distinct  gyrus  only  when  the 
lateral  orbital  sulcus  is  long,  is  situated  external  to  the  H-shaped 
sulcus.  It  is  continuous  with  both  middle  and  inferior  frontal 
gyri  at  the  superciliary  border  of  the  hemisphere. 

The  Island  (of  Reil),  Inferior  Surface  (Fig.  26). — If  the  an- 
terior part  of  the  temporal  lobe  be  removed,  the  under  surface 
of  the  island  (insula)  is  brought  into  view.     The  circular  sulcus 


THE    BASE    OF    THE    FORE-BRAIN. 


75 


.K«& 


■^7-ERAL\^ 


Fig.  26. — Base  of  fore-brain  and  cut  surface  of  mid-brain.     Right  temporal  pole  cut 
away,  to  show  inferior  surface  of  the  island.     {Original.) 

a.  Sulcus  parolfactorius  anterior,  b.  Sulcus  parolfactorius  posterior,  c.  Olfactory  bulb, 
d.  Olfactory  tract,  e.  Olfactory'  stria;,  f.  Area  parolfactoria.  g.  Trigonum  olfactorium. 
h.  Substantia  perforata  anterior,  i.  Gyrus  subcallosvis  (peduncle  of  corpus  callosum). 
j.  Optic  chiasma.  k.  Optic  tract.  1.  Tuber  cinereum.  m.  Infundibulum.  n.  Corpus  mam- 
millare.  o.  Substantia  perforata  posterior,  p.  Aqueductus  cerebri,  q.  Quadrigeminal  col- 
liculus.    r.  Corpus  pineale.     s.  Spleniuin. 


THE    BASE    OF   THE    FORE-BRAIN.  77 

bounds  it  on  two  sides  and  separates  it  from  the  posterior  orbital 
gyrus,  in  front;  and  from  the  temporal  lobe,  behind.  Laterally 
it  is  separated  from  the  frontal  and  the  parietal  parts  of  the  oper- 
culum by  an  antero-posterior  cleft  continuous  with  the  lateral 
cerebral  fissure. 

The  insula  is  continuous  with  the  anterior  perforated  substance, 
and  the  area  of  transition  from  one  to  the  other  is  called  the 
threshold,  or  limen  insulcE  (Fig.  26). 

Rhinencephalon. — The  smelling  brain  belongs  to  the  basal 
surface.  It  is  rudimentary  in  man.  Many  connected  parts 
make  it  up.  It  is  divided  into  two  parts  by  the  sulcus  parolfac- 
torius  posterior.  These  are  designated  as  the  pars  anterior  rhin- 
encephali  and  the  pars  posterior  rhinencephali.  The  pars 
anterior  of  the  rhinencephalon  embraces,  'first,  the  olfactory  lobe, 
which  is  made  up  of  the  olfactory  bulb,  tract,  triangle  and  the 
medial  and  intermediate  striae;  and  second,  the  area  parolfactoria. 
In  the  pars  posterior  rhinencephali  are  included  the  anterior 
perforated  substance,  the  gyrus  subcallosus,  the  lateral  olfactor}^ 
stria,  and  the  limen  insulae. 

Olfactory  Lobe.  {Lobus  olfactorius). — ^There  is  one  lobe  that 
is  studied  only  on  the  basal  surface  of  the  fore-brain.  That  is  the 
olfactory  lobe  (Fig.  26).  Belonging  to  the  pars  anterior  rhinen- 
cephali, it  comprises  many  connected  parts;  and  the  reason  for 
calling  them  the  olfactory  lobe  is  found  in  the  lower  animals 
and  in  the  human  embryo,  where  it  exists  as  a  prominent  hollow 
process  of  the  cerebral  hemisphere  (Figs.  17  and  18). 

Bulbus  olfactorius 
Tractus  olfactorius 
Olfactory  Lobe  I    Trigonum  olfactorium 
Stria  medialis 
,  Stria  intermedia. 

The  olfactory  bulb  {bulbus  olfactorius)  is  an  ovoid  mass  of 
brain  matter  about  half  an  inch  long,  one-sixth  of  an  inch  wide 
and  a  quarter  of  an  inch  in  vertical  diameter  (Fig.  26).  It  is 
lodged  in  the  olfactory  sulcus  of  the  frontal  lobe  and  rests  upon 
the  cribriform  plate  of  the  ethmoid  bone  through  which  it  receives 
the  twenty  or  thirty  olfactory  nerves.     The  center  of  the  bulb 


78  THE    CEREBRUM. 

is  formed  by  a  gray  core  derived  from  the  ependymal  lining  of  the 
embryonic  ventricle.  The  gray  core  is  surrounded  by  a  white 
sheath  of  meduUated  fibers  running  longitudinally;  posterior 
to  the  bulb  these  fibers  form  the  olfactory  tract.  Five  layers  of 
gray  substance  thicker  on  the  ventral  side,  surround  the  vi^hite 
sheath  and  constitute  the  surface  of  the  bulb.  The  gray  sub- 
stance forms  the  terminal  nucleus  of  the  olfactory  nerves  and  gives 
origin  to  the  fibers  of  the  olfactory  tract. 

Olj actor y  Tract  {Tr actus  olfactorius). — ^The  tract  is  triangular 
in  section,  slightly  more  than  an  inch  long  and  one  line  in  width 
(Fig.  26).  It  is  partially  concealed  in  the  olfactory  sulcus,  and 
is  a  continuation  backward  of  the  medullated  mitral  axones  which 
ensheath  the  gray  core  of  the  olfactory  bulb.  At  its  posterior  end 
the  olfactory  tract  divides  into  three  striae — lateral,  intermediate 
and  medial,  two  of  which  are  easily  seen.  These  stricB  oljactorim 
are  continuous  with  the  three  angles  of  the  tract.  The  lateral 
and  medial  strias  diverge  and  inclose  the  olfactpry  triangle  between 
them.  The  lateral  stria  {stria  lateralis)  courses  outward  and 
backward  and  terminates  in  the  uncus  at  the  anterior  extremity- 
of  the  hippocampal  gyrus.  According  to  Retzius,  the  lateral' 
olfactory  stria  terminates  in  the  rudimentary  gyri,  circumamhiens 
and  semilunaris,  which  form  the  anterior  end  of  the  hippocampal 
gyrus.  The  lateral  stria  bounds  on  the  outer  side  the  anterior 
perforated  space.  The  medial  stria  {stria  medialis)  bends  sharply 
inward,  toward  the  median  line,  and  runs  between  the  triangle 
and  parolfactory  area  (of  Broca).  Its  fibers  turn  into  Broca's 
area  and  the  gyrus  cinguli,  chiefly,  but  some  of  them  enter  the 
triangle,  the  gyrus  subcallosus,  and  the  hippocampus  through 
septum  pellucidum  and  fornix.  Thus  the  medial  and  lateral 
striae  unite  the  opposite  ends  of  the  gyrus  fomicatus.  From  the 
dorsal  angle  of  the  olfactory  tract,  a  bundle  of  fibers  proceeds 
into  the  triangle  and  frontal  lobe,  constituting  the  intermediate 
stria  {stria  intermedia).  The  intermediate  olfactory  stria  is  often 
not  visible  on  the  surface,  as  it  turns  at  once  upward  into  the 
frontal  lobe.  Upon  reaching  the  level  of  the  anterior  commissure, 
it  passes  through  that  commissure  to  the  opposite  hemisphere, 
where  it  divides  into  two  bundles;  one  of  which  (the  commissural 


THE    BASE    OF    THE    FORE-BRAIN.  79 

bundle)  turns  down  into  llic  intermediate  stria  of  the  opposite 
olfactory  tract,  and  the  other  (the  decussating  bundle)  runs  back- 
ward and  outward  toward  the  uncinate  region  of  the  limbic  lobe. 

The  Olfactory  Triangle  and  the  Parolfactory  Area  (of  Broca). — 
The  triangular  portion  of  the  cortex  between  the  medial  and 
lateral  olfactory  striae,  called  the  triangle  (trigonum  olfactorium) 
is  continuous  medially  \\dth  the  area  par olf actor ia.  The  medial 
stria  marks  the  boundary  between  them  (Figs.  26  and  27).  Both 
are  bounded  behind  by  the  sulcus  parol factorius  posterior  (trans- 
verse part),  and  the  oblique  part  of  the  same  fissure  separates  the 
parolfactory  area  from  the  gyrus  subcallosus  (peduncle  of  the 
corpus  callosum).  The  area  parolfactoria  (Brocae)  is  limited 
in  front  by  a  slight  curved  depression,  the  sulcus  parolfactorius 
anterior.     On  the  medial  surface,  this  area  joins  the  g}Tus  cinguli. 

The  anterior  perforated  substance  (substantia  perforata  anterior) 
of  the  pars  posterior  rhinencephali  requires  further  mention  (Fig. 
26).  It  is  separated  from  the  triangle  by  a  very  faint  groo\-e, 
the  posterior  sulcus  parolfactorius.  Medially,  it  is  in  direct  con- 
tinuity mth  the  tuber  cinereum.  The  optic  tract  bounds  it, 
postero-medially.  Laterally,  it  forms  the  linien  insulce  in  the 
floor  of  the  fossa  cerebri  lateraUs,  where  it  is  overlapped  by 
the  temporal  lobe.  Superiorly,  it  is  continuous  with  the  base 
of  the  corpus  striatum.  Coursing  along  the  inner  and  outer 
border  of  the  anterior  perforated  substance  are,  respectively,  the 
gyrus  subcallosus  and  lateral  olfactory  stria,  which  con\'erge  and 
meet  in  the  hippocampal  gyrus.  The  perforations  of  this  area 
are  for  the  antero-lateral  ganglionic  arteries. 

Tentorial  Area  of  the  Basal  Surface  (Figs.  26,  24  and  28). — 
From  the  temporal  pole  backward,  the  basal  surface  of  the  cere- 
bral hemisphere  presents  three  nearly  parallel  g}'ri,  viz.,  the 
inferior  temporal  gyrus,  which  forms  the  infero-lateral  border; 
the  fusiform  gyrus,  the  middle  one,  and  the  gyrus  hippocampi 
which  hes  next  the  mid-brain.  The  last  belongs  to  the  g}'rus 
fomicatus  of  the  limbic  lobe;  it  is  continuous,  posteriorly,  with 
the  lingual  gyrus,  which  forms  a  part  of  the  medial  occipital 
border  of  the  cerebral  hemisphere.  The  fusiform  and  inferior 
temporal  gyri  belong  to  the  inferior  surface  of  the  temporal  and 


8o  THE    CEREBRUM. 

occipital  lobes.  These  two  lobes  are  directly  continuous  with 
each  other  on  their  inferior  surfaces,  and  are  only  separated  arbi- 
trarily by  an  imaginary  line  drawn  from  the  preoccipital  notch 
to  the  anterior  end  of  the  calcarine  fissure.  They  are  only  partially 
separated  from  the  gyrus  hippocampi;  the  ectorhinal  sulcus 
(s.  rhinalis)  and  the  anterior  part  of  the  collateral  fissure  He 
between  the  temporal  lobe  and  the  hippocampal  gyrus-  of  the 
limbic  lobe;  while  the  inferior  surface  of  'the  occipital  lobe  is 
separated  from  the  gyrus  cinguli,  of  the  limbic  lobe,  by  the  anterior 
calcarine  fissure.  The  fissures  and  sulci  of  the  tentorial  area 
are  the  following: 

Chorioidal  fissure  (f.  chorioidea) 

Hippocampal  fissure  (f.  hippocampi) 

Ectorhinal  sulcus  (s.  ectorhinalis) 

Collateral  fissure  (f.  collateralis) 

Inferior  temporal  sulcus  (s.  temporalis  inferior). 

The  chorioidal  fissure  (/.  chorioidea)  forms  a  part  of  the 
medial  boundary  of  the  tentorial  area  (Figs.  26  and  28).  At  the 
surface  it  appears  to  be  identical  with  the  hippocampal  fissure; 
but,  upon  looking  deeper,  the  two  are  found  to  be  separated  by 
the  fascia  dentata  and  the  crus  of. the  fornix.  This  fissure  is 
separated  from  the  inferior  horn  of  the  lateral  ventricle,  only  by  a 
layer  of  epithelium,  derived  from  the  roof  plate  of  the  telencepha- 
lon.    It  contains  the  chorioid  plexus  of  the  inferior  horn. 

Hippocampal  Fissure.  {F.  hippocampi,  Fig.  28). — Along  the 
medial  and  concave  border  of  the  hippocampal  gyrus  is  the  cres- 
centic  fissure  known  as  the  hippocampal  fissure.  The  fissure 
in  front  is  closed  by  the  uncus.  It  extends  backward  to  the 
splenium  of  the  corpus  callosum  where,  in  the  adult,  it  is  con- 
tinuous with  the  furrow  behind  and  above  the  corpus  callosum, 
called  the  callosal  sulcus.  The  hippocampal  is  a  true  fissure  as 
it  indents  the  whole  ventricular  wall;  the  long  ventricular  eminence 
produced  by  it  is  the  hippocampus  seen  in  the  inferior  horn  of 
the  lateral  ventricle  (see  medial  surface  of  the  cerebral  hemisphere). 

Ectorhinal  Sulcus.  (Jncisura  temporalis,  Figs.  26  and  29). — 
Midway  between  the  temporal  pole  and  the  hook-point  of  the 
hippocampal  gyrus  is  a  slight  notch,  called  the  ectorhinal  sulcus. 


THE    BASE    OF   THE    FORE-BRAINj*  8l 

which  represents  an  important  lateral  boundary  of  the  rhinen- 
cephalon  in  animals  with  highly  developed  sense  of  smell.  It 
indicates  in  man  the  boundary  between  the  hippocampal  and 
fusiform  gyri.  A  half  inch  behind  the  ectorhinal  sulcus  is  the 
anterior  end  of  the  collateral  fissure. 

Fissura  Collateralis  (Figs.  26  and  28). — ^The  collateral  fissure 
extends  in  a  somewhat  curved  course  from  near  the  temporal 
pole  almost  to  the  occipital  pole.  Its  anterior  two-thirds  separates 
the  hippocampal  from  the  fusiform  gyrus;  its  posterior  one- third 
completes  the  medial  and  upper  boundary  of  the  fusiform  gyrus 
and  separates  it  from  the  g}^rus  lingualis. 

Inferior  Temporal  Sulcus  (Fig.  26). — Only  one  sulcus  belongs 
wholly  within  the  inferior  surface  of  the  temporal  and  occipital 
lobes.  It  extends  from  a  point  near  the  occipital  pole  forward 
along  the  infero-lateral  border  of  the  hemisphere  almost  to  the 
temporal  pole,  and  incompletely  separates  the  inferior  temporal 
gyrus  and  the  lateral  occipital  gyrus  from  the  gyrus  fusiformis. 
Very  frequently  the  sulcus  has  two  or  more  interruptions.  It 
may  be  called  the  temporo-occipital  sulcus. 

Gyrus  Fusiformis. — One  gyrus  only  is  found  entirely  \^■ithin 
the  inferior  temporo-occipital  region  (Figs.  26  and  29).  That 
is  the  fusiform  (temporo-occipital  gyrus).  It  extends  from  near 
the  occipital  pole  forward  and  forms  the  temporal  pole.  The 
posterior  nine-tenths  of  its  medial  boundar}^  is  formed  by  the 
collateral  fissure  and  the  anterior  one-tenth  by  an  imaginary  line 
and  the  ectorhinal  sulcus;  laterally,  it  is  bounded  by  the  inferior 
temporal  sulcus. 

Gyrus  Lingualis. — ^The  g}^rus  linguahs  hes  above  and  medial 
to  the  posterior  one-third  of  the  collateral  fissure;  inferior  and 
lateral  from  the  calcarine  fissure.  It  is  continuous  with  the  gyrus 
hippocampi  of  the  limbic  lobe  in  front.  The  gyrus  lingualis 
(Fig.  29)  forms  nearly  all  of  the  medial  occipital  border  of  the 
hemisphere.  It  contains  a  part  of  the  receptive  visual  center 
(Figs.  55  and  57). 

Limbic  Lobe  (Lobus  Limbus),  Inferior  Part. — ^The  gyrus 
hippocampi  of  this  lobe  is  visible  on  the  inferior  surface  of  the 
fore-brain  (Fig.  26).  Notice  how  this  crescentic  gyrus  embraces 
6 


82  THE    CEREBRUM. 

in  its  concavity  the  section  of  the  mid-brain.  It  is  separated  from 
the  fusiform  gyrus  by  the  collateral  fissure  and  the  ectorhinal 
sulcus;  and  bounded  medially  by  the  hippocampal  fissure.  The 
anterior  end  of  the  gyrus  is  flexed  inward  and  backward  over  the 
end  of  the  hippocampal  fissure  and  the  whole  anterior  part  consti- 
tutes the  uncus  hippocampi.  The  region  of  the  uncus  is  some- 
what irregular  and  appears  to  comprise  the  gyrus  circumamhiens 
and  the  gyrus  semilunaris  described  by  Retzius.  It  represents 
the  greater  part  of  the  lobus  pyraformis  of  osmatic  mammals 
and  is  probably  the  chief  receptive  center  of  smell;  it  receives  the 
lateral  stria  of  the  olfactory  tract  and  fuses  with  a  low  oblique 
ridge,  the  gyrus  subcallosus  (or  peduncle  of  the  corpus  callosum). 

If  the  hippocampal  gyrus  be  drawn  downward  somewhat,  a 
rudimentary  gyrus  may  be  seen  between  the  hippocampal  and 
chorioidal  fissures.  That  is  the  dentate  fascia.  It  is  continuous 
with  the  reflected  part  of  the  uncus  in  front,  and  behind  is  in  con- 
tinuity with  the  fasciola  cinerea  and  gyrus  supracallosus.  Like 
the  hippocampal  gyrus  it  forms  a  part  of  the  limbic  lobe.  We 
shall  recur  to  this  lobe  on  the  medial  surface  of  the  hemisphere. 

Having  studied  the  basal  structures  of  the  cerebral  hemispheres, 
it  is  now  in"order  to  examine  the  median  structures  in  the  inferior 
surface  of  the  fore-brain.  They  occupy  the  interpeduncular  or 
hypophyseal  region.  They  constitute  the  hypothalamus  and 
form  part  of  the  floor  of  the  third  ventricle. 

The  hypothalamus  is  the  name  applied  to  the  fore-brain 
structures  under  the  thalamus.  Posteriorly  it  blends  with  the 
mid-brain.  Its  free  portion  is  divided  into  two  parts,  viz.,  the 
pars  optica  hypothalami  and  the  pars  mammillaris  hypo- 
thalami. The  former  belongs  to  the  telencephalon,  the  latter  to 
the  diencephalon.     They  include  the  following: 


Pars  Optica  Hypothalami 


Lamina  cinerea  terminalis 

Optic  chiasma  (chiasma  opticum) 

Tuber  cinereum 

Infundibulum  and 

Hypophysis. 


Pars  Mammillaris  Hypothalami  <    Corpora  mammillaria. 


THE    BASE    OF    THE    EORE-BRAIN.  83 

The  lamina  cinerea  terminalis  (Fig.  27)  is  most  superior 
of  the  median  structures.  It  is  a  thin  kimina  of  ash-colored 
(cinereum)  gray  matter  closing  the  end  of  the  neural  tube.  It 
extends  from  the  anterior  superior  surface  of  the  optic  chiasma 
upward  and  backward  to  the  anterior  commissure,  just  in  front 
of  which  it  becomes  continuous  with  the  lamina  rostralis  of  the 
corpus  callosum.  Laterally,  it  is  continuous  with  the  cortex 
of  the  cerebral  hemisphere.  Behind  it,  is  the  third  ventricle; 
in  front  of  it,  a  part  of  the  longitudinal  fissure  of  the  cerebrum. 

Optic  Chiasma.  {Chiasma  opticiim). — ^The  optic  chiasma  is 
a  quadrilateral  sheet  of  nerve  fibers  whose  anterior  angles  recei\-e 
the  optic  nerves  and  whose  posterior  angles  gi\'e  off  the  optic 
tracts  (Fig.  21).  With  the  nerves  and  tracts  attached,  it  is  x- 
shape.  The  chiasma  is  a  median  structure  and  is  situated  beneath 
the  lamina  cinerea,  in  the  optic  groove  of  the  sphenoid  bone. 
The  fibers  of  the  optic  nerves  and  tracts  compose  it.  There  are 
three  sets  of  these  fibers,  namely,  the  intercerehral,  the  direct, 
and  the  decussating.  A  fourth  group  of  fibers,  called  the  inter- 
retinal  and  said  to  be  commissural  for  the  retince,  has  been  hither- 
to described,  but  their  existence  is  very  doubtful.  The  inter- 
cerebral  fibers  are  not  found  in  the  optic  nerves,  but  form  the 
inferior  commissure  (Guddeni)  which  joins  together  the  medial 
geniculate  bodies  (Fig.  43).  The  direct  (or  temporal)  and  decus- 
sating (or  nasal)  fibers  run  through  nerve  and  tract  and  join  the 
retina  with  the  brain  on  the  same  and  the  opposite  side,  respectively 
In  most  vertebrates  below  mammals,  and  in  the  mouse  and  guinea 
pig,  it  is  said  that  the  optic  fibers  aU  decussate  in  the  cliiasma. 
Normally  in  man  and  the  higher  mammals,  the  temporal  half 
of  each  retina  contributes  to  the  chiasma  direct  fibers  and  the 
nasal  half  crossed  fibers  (Fig.  67).  The  optic  nerves  (ncrvi 
optici)  extend  from  the  foramen  scleras  of  each  eyeball  back  to 
the  front  of  the  chiasma,  through  the  optic  foramina;  they  rise 
in  the  gangHonar  cells  of  the  retinae,  which  are  connected  with 
the  rods  and  cones  by  the  bipolar  neurones.  The  optic  tracts 
(tra£tus  optici)  connect  the  chiasma  with  the  brain.  Each  tract 
winds  outward  and  backward  around  the  cerebral  peduncle, 
and  divides  into  a  medial  and  a  lateral  root  (Fig.  43).     The  roots 


84  THE    CEREBRUM. 

wind  under  the  thalamus  and  disappear  at  the  corresponding 
geniculate  body.  The  lateral  root  contains  all  the  retinal  fibers, 
the  medial  root  has  nothing  to  do  with  vision.  The  fibers  of  the 
lateral  root  {radix  lateralis)  may  be  traced  to  the  lateral  geniculate 
body  (80  per  cent.,  Von  Monokow),  to  the  pulvinar  of  the  thalamus 
(nearly  all  the  20  per  cent,  remaining),  and  the  rest  to  the  superior 
quadrigeminal  colliculus.  The  optic  radiation  of  the  capsule  con- 
nects these  centers  with  the  medial  occipital  cortex.  The  medial 
root  rises  and  ends  in  the  medial  geniculate  body  and  thalamus. 
Its  fibers  form  the  commissura  inferior  (Guddeni). 

Tuber  Cinereum. — ^The  posterior  border  of  the  optic  chiasma 
is  continuous  with  the  tuber  cinereum  (Figs.  21  and  26).  Here 
the  gray  matter  is  thickened  and  centrally  prominent.  The 
bulbous  infundibulum  projects  downward  from  it  to  rest  in  the 
sella  Turcica,  where  it  forms  the  posterior  lobe  of  the  hypophysis. 
The  upper  end  of  the  infundibulum  is  hollow  (funnel-like).  Its 
cavity  forms  the  lowest  part  of  the  third  ventricle.  In  man  the 
bulb  of  the  infundibulum  is  solid  at  maturity,  though  hollow  in 
the  embryo.  It  is  composed  largely  of  fibrous  tissue,  notwith- 
standmg  the  fact  that  it  is  developed  from  the  floor  of  the  telen- 
cephalon. From  the  base  (superior  end)  of  the  infundibulum, 
the  tuber  cinereum  extends  in  continuity  with  the  anterior  per- 
forated substance  on  each  side  of  it;  and,  behind,  the  corpora 
mammillaria  mark  the  boundary  between  it  and  the  posterior 
perforated  substance  of  the  mid-brain. 

The  lamina  cinerea  and  tuber  cinereum  form  the  inferior  gray 
commissure  of  the  fore-brain. 

The  hypophysis  (pituitary  body.  Fig.  21)  is  composed  of  two 
lobes  bound  together  by  connective  tissue.  A  sheet  of  dura  mater 
(diaphragma  sellce)  holds  them  in  the  hypophyseal  fossa.  The 
anterior  lobe,  the  larger,  is  derived  from  the  epithelium  of  the 
mouth  cavity;  and,  in  structure,  resembles  the  thyroid  gland.  Its 
closed  vesicles,  lined  with  columnar  epithelium  (in  part  ciHated), 
contains  a  viscid  jelly-like  material  (pituita),  which  suggested  the 
old  name  for  the  body.  The  anterior  lobe  is  hollowed  out  on 
its  posterior  surface  (kidney- shape)  and  receives  the  posterior 
lobe,    the    infundibulum,    into    the    concavity.     The    hypophysis 


THE    BASE    OF    THE    FORE-BRAIN.  85 

has  an  internal  secretion  which  appears  to  have  an  inhibitive 
action  on  gro^^i:h  and  has  been  found  diseased  in  acromegalia. 

Corpora  Mammillaria  (Figs.  21  and  26). — ^Two  white  bodies 
(corpora  albicantia),  as  large  as  a  small  pea,  are  situated  one  on 
either  side  of  the  median  Une,  between  the  tuber  cinereum  and 
the  pigmented  gray  matter  of  the  posterior  perforated  substance. 
Each  is  formed  superficially  by  a  loop  in  the  columna  of  the  fornix 
and  is,  therefore,  composed  of  white  substance  at  the  surface. 
There  is  gray  matter  in  the  interior  which  forms  a  medial  and  a 
lateral  nucleus  (Fig.  46).  In  the  medial  nucleus  the  fornix  fibers 
terminate  and  an  ascending  bimdle  rises,  called  the  fasciculus 
thalamo-mammillaris  (Vicq  d'Azyri).  The  latter  terminates  in 
the  anterior  nucleus  of  the  thalamus.  From  the  medial  nucleus 
of  the  corpus  mamillare  also  rises  the  tegmental  part  of  the  fascic- 
ulus pedunculo-mammillaris;  the  basilar  portion  of  the  same 
bundle  rises  in  the  lateral  nucleus  and  both  parts  of  this  pedunculo- 
mammillary  bundle  run  downward  into  the  mid-brain  to  an 
unknown  termination. 

Immediately  behind  the  corpora  mammillaria  is  the  posterior 
perforated  substance  (Figs.  21  and  26).  This  is  the  exposed 
part  of  the  substantia  nigra  of  the  mid-brain,  perforated  for  the 
passage  of  the  postero-median  ganghonic  arteries.  The  pons 
and  bases  pedunculi  bound  it  behind.  Issuing  from  the  inner 
side  of  the  basis  pedunculi  is  the  large  oculomotor  ner\'e;  and 
coursing  over  its  surface  from  behind  forward,  is  the  smaller 
trochlear  nerve.  The  bases  pedunculi  ^^ill  be  described  ^^ith 
the  mid-brain  to  which  they  belong. 

FISSURES  OF  THE  MEDIAL  AND  TENTORIAL  SURFACE. 

To  expose  the  medial  surface  of  the  cerebral  hemispheres,  a 
median  sagittal  section  must  be  made  through  the  connecting 
Hnks  of  the  hemispheres  and  the  inter-brain,  dividing  the  fore- 
brain  into  lateral  halves.  Separate  the  Hps  of  the  longitudinal 
fissure  of  the  cerebrum;  drop  the  moistened  brain- knife  do\Mi 
onto  the  corpus  callosum;  and  make  one  quick  sweep  of  the 
knife  toward  you.  Of  the  surface  now  exposed  the  middle  one- 
tliird  is  produced  by  section. 


86  THE    CEREBRUM. 

It  is  convenient  to  study  the  tentorial  area  of  the  basal  surface 
with  the  medial  surface  (Fig.  26).  In  this  medial  and  tentorial 
surface  there  are  six  important  sulci  and  four  fissures  (Fig.  28). 

Of  cingulum  (s.  cinguli) 
Callosal  (s.  corporis  callosi) 
Subparietal  (s.  subparietalis) 
Occipito -parietal  (s.  occipito-parietalis) 
Inferior  temporal  (s.  temporalis  inferior) 
Ectorhinal  (s.  ectorhinalis). 


Sulci 


Fissures 


Calcarine  (fissura  calcarina) 
Hippocampal  (f.  hippocampi) 
Chorioidal  (f.  chorioidea) 
Collateral  (f.  collateralis). 


Sulcus  Cinguli  (Calloso-marginal  Sulcus). — ^Beginning  under 
the  middle  cut  surface  and  extending  in  a  curve  forward,  upward, 
and  backward,  until  it  half  encircles  the  corpus  callosum;  and, 
then,  turning  upward  to  the  supero-medial  border  and  ending 
just  behind  the  central  sulcus  is  the  sulcus  cinguli  (Figs.  27  and  28). 
It  separates  the  gyrus  cinguli  and  a  marginal  gyrus,  including 
the  straight  and  superior  frontal,  from  one  another  by  its  anterior 
part;  and,  by  its  marginal  end,  separates  the  paracentral  lobule 
from  the  prsecuneus.  The  sulcus  cinguH  is  usually  interrupted 
by  one  annectant  gyrus  and  often  by  two.  These  indicate  its 
development  in  three  separate  parts. 

At  its  beginning  under  the  corpus  callosum,  the  sulcus  cinguH 
is  almost  continuous  with  a  small  curved  sulcus,  which  runs 
nearly  vertically  downward,  called  the  anterior  parolfactory- 
sulcus  (Figs.  28  and  29).  Behind  that  httle  sulcus  there  is  a 
small  curved  gyrus,  the  parolfactory  area  (of  Broca),  which  is 
continuous  with  the  gyrus  cinguli  and  bounded  behind  by  another 
slight  sulcus,  called  the  posterior  parolfactory  sulcus.  The 
latter  separates  the  area  parolfactoria  from  the  gyrus  subcallosus. 

Subparietal  Sulcus. — About  one  inch  above  and  behind  the 
posterior  end  of  the  corpus  callosum  there  is  an  irregular  sulcus, 
called  the  subparietal,  which  separates  the  gyrus  cinguli  of  the 
limbic  lobe  from  the  prsecuneus  of  the  parietal  lobe  (Fig.  28). 

The    callosal   sulcus  is  the  deep  furrow  between  the  corpus 


FISSURES    OF    THE    MEDIAL    AND    TENTORIAL    SURFACE. 


87 


THE    BASE    OF    THE    FORE-BRAIN.  89 

callosum  and  the  gyrus  cinguli.  It  follows  the  convexity  of  the 
corpus  callosum  and  was  formerly  called  the  ventricle  of  it  CFig. 
28).  The  callosal  sulcus,  behind  the  corpus  callosum,  is  continu- 
ous with  the  liippocampal  fissure. 

The  occipito-parietal  sulcus  (Figs.  27,  28  and  20),  the  inter- 
nal part,  extends  downward  from  the  supero-medial  border  to 
the  middle  of  the  calcarine  fissure.  The  two  form  a  lambda- 
shaped  fissure  ^  (Fig.  28);  the  lambda  being  tilted  toward  the 
frontal  pole  has  one  anterior  and  two  posterior  rami.  The  anterior 
ramus  and  the  lower  of  the  posterior  rami  constitute  the  calcarine 
fissure;  the  posterior  superior  ramus,  is  the  occipito-parietal 
sulcus.  This  latter  sulcus  cuts  the  supero-medial  border  at  the 
junction  of  the  posterior  one- sixth  with  the  anterior  five-sixths 
of  that  border;  it  is  situated  about  two  inches  above  the  occipital 
pole,  and  hes  one-sixth  of  an  inch  anterior  to  the  point  in  the 
skull  called  the  lambda.  It  separates  the  parietal  lobe  from  the 
cuneus  of  the  occipital  lobe.  The '  occipito-parietal  sulcus  is  a 
deep  one.  In  the  embryo  the  primary  occipito-parietal  fissure 
produces  an  eminence  in  the  posterior  horn  of  the  lateral  ven- 
tricle (Cunningham).  It  is  then  a  true  fissure.  But  that  prim- 
itive fissure  and  the  ventricular  eminence  entirely  disappear, 
and  the  adult  sulcus  is  a  secondary  and  superficial  furrow, 
hence  it  is  properly  called  a  sulcus  and  not  a  fissure.  At  the 
inferior  end  of  the  occipito-parietal  sulcus  a  buried  annectant 
gyrus,  the  gyrus  cunei,  separates  the  occipito-parietal  sulcus 
from  the  calcarine  fissure,  with  w^hich  superficially  it  is  contin- 
uous. 

The  calcarine  fissure  begins  a  quarter  of  an  inch  below  the 
posterior  end  of  the  corpus  callosum  and  runs  backward  and 
slightly  upward  to  the  lower  end  of  the  occipito-parietal  sulcus; 
and,  then,  curves  downward  to  a  point  near  the  occipital  pole; 
where  it  ends  bifid  (Figs.  28  and  26).  It  is  thus  divided  by  the 
sulcus  occipito-parietalis  into  an  anterior  calcarine  and  a  posterior 
calcarine  fissure.  These  three  furrows  are  continuous  with  one 
another  superficially  in  the  human  brain;  but  buried  annectant 
g\'ri  actually  separate  them  from  each  other:  the  gyrus  cunei 
separates  the  occipito-parietal  sulcus  from  the  calcarine  fissure 


90  THE    CEREBRUM. 

and  the  anterior  calcarine  fissure  is  separated  from  the  posterior 
calcarine  by  the  gyrus  cuneo-lingualis  (Cunningham).  The 
anterior  calcarine  fissure  indents  the  medial  wall  of  the  posterior 
horn  of  the  lateral  ventricle,  producing  the  calcar  avis. 

Hippo c amp al  Fissure  (Figs.  26  and  28). — A  crescentic  fissure, 
convex  downward  begins  under  the  splenium  of  the  corpus  cal- 
losum  in  continuity  with  the  callosal  sulcus,  and  winds  forward 
beneath  the  thalamus  to  within  an  inch  of  the  temporal  pole, 
where  it  is  closed  by  the  uncus.  It  is  the  hippocampal  fissure. 
On  the  surface  of  the  temporal  lobe  this  fissure  appears  to  be 
identical  with  the  temporal  extension  of  the  chorioidal  fissure;  but, 
deeply,  it  lies  posterior  to  that  fissure  and  is  separated  from  it 
by  the  fascia  dentata.  The  hippocampal  fissure  produces  a  long 
ridge  in  the  inferior  horn  of  the  lateral  ventricle,  called  the  hip- 
pocampus. 

The  chorioidal  fissure  (Figs.  28  and  39)  describes  about 
two-thirds  of  a  circumference  along  the  concavity  of  the  fornix. 
It  extends  from  the  foramen  interventriculare  backward  over 
the  thalamus;  and  then  downward  and  forward  along  the  hip- 
pocampal fissure,  but  separated  from  it  by  the  dentate  fascia.  The 
chorioidal  fissure  is  a  complete  one,  involving  the  whole  hemisphere 
wall.  A  single  layer  of  epithelium  separates  it  from  the  lateral 
ventricle.  The  pia  mater,  dipping  into  it,  forms  the  chorioid 
plexus  of  that  ventricle.  The  fissure  is  peculiar  in  the  fact  that 
between  the  inter-brain  and  the  fornix  there  is  a  transverse  slit 
by  means  of  which  it  is  continuous  with  the  same  fissure  on  the 
opposite  side.  In  this  antero-superior  part,  which  is  in  direct 
continuity  with  the  transverse  fissure  of  the  cerebrum,  is  the  border 
of  the  chorioid  tela  of  the  third  ventricle. 

Collateral  Fissure.-^The  collateral  is  a  long  fissure  (Figs. 
26  and  28).  It  reaches  from  near  the  occipital  almost  to  the 
temporal  pole.  It  is  situated  below  and  parallel  with  the  cal- 
carine and  hippocampal  fissures,  being  separated  from  the  former 
by  the  hngual  gyrus  and  from  the  latter  by  the  hippocampal  gyrus. 
The  gyrus  fusiformis  lies  below  and  external  to  this  fissure.  Ante- 
rior to  the  collateral  fissure,  there  is  a  small  sulcu'fe  between  the 
gyrus  hippocampi  and  the  temporal  pole,  called  the  ectorhinal 


THE    BASE    OF    THE    PORE- BRAIN. 


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LOBES  AND  GYRI  OF  MEDIAL  AND  TENTORIAL  SURFACE.   93 

sulcus,  which  represents  a  very  important  fissure  (/.  rhinalis) 
in  osmatic  animals.  The  collateral  fissure  is  occasionally  inter- 
rupted by  two  annectant  gyri  and  divided  into  a  temporal,  an 
occipital  and  an  intermediate  part.  This  signifies  a  persistence 
of  its  embryonic  condition.  The  intermediate  portion,  some- 
times assisted  by  the  anterior  part,  indents  the  ventricular  wall 
and  produces  the  emlnentia  collateraUs  in  the  inferior  horn  of 
the  lateral  ventricle. 

The  inferior  temporal  sulcus  is  usually  a  series  of  indenta- 
tions rather  than  a  continuous  sulcus  (Figs.  26  and  28).  It  is 
about  equal  in  extent  to  the  collateral  fissure  from  which  it  is 
separated  by  the  fusiform  gyrus.  It  is  parallel  with  the  infero- 
lateral  border  of  the  cerebral  hemisphere.  As  the  inferior  tem- 
poral gyrus,  which  forms  this  border  reaches  over  onto  the  ten- 
torial area  a  variable  distance,  even  in  the  two  sides  of  the  same 
brain,  the  position  of  the  inferior  temporal  sulcus  it  not  constant ; 
but  it  is  usuaUy  one-quarter  or  one-half  inch  medial  to  the  border. 

LOBES  AND  GYRI  OF  MEDIAL  AND  TENTORIAL 
SURFACE. 

The  gyri  form  two  concentric  rings,  interrupted  antero-inferiorly 
at  the  fossa  cerebri  lateralis,  which  encircle  the  corpus  callo- 
sum  and  thalamus  (Fig.  28).  The  two  rings  are  separated  from 
one  another  by  a  broken  fissure,  the  limbic  fissure,  made  up  of 
the  sulcus  cinguh  (except  its  marginal  end),  the  subparietal  sulcus, 
and  the  anterior  part  of  the  calcarine  and  of  the  collateral  fissures. 

Gyrus  Fornicatus. — ^The  gyrus  cinguli  and  the  gyrus  hippo- 
campi, joined  together  at  the  posterior  border  of  the  corpus  cal- 
losum  by  the  Isthmus,  and  together  constituting  the  gyrus  forni- 
catus, form  the  central  ring.  The  gjTUS  cinguli  begins  anteriorly 
under  the  corpus  callosum  in  continuity  with  the  area  parolfac- 
toria  anterior  to  the  fossa  cerebri  lateralis;  and  the  hippocampal 
terminates  as  uncus  just  behind  that  fossa.  The  gyrus  fornicatus 
forms  the  chief  part  of  the  limbic  lobe. 

The  gyrus  cinguli  is  the  arched  gyrus  which  is  inclosed  between 
the  callosal  sulcus  and  the  sulcus  cinguli,  except  above  the  posterior 


94  THE    CEREBRUM. 

end  of  the  corpus  callosum;  there  it  is  bounded  on  its  convexity 
by  the  subparietal  sulcus  (Fig.  28).  Underneath  the  corpus 
callosum,  the  anterior  end  of  the  gyrus  cinguli  is  continuous  with 
a  small  vertical  gyrus,  called  the  area  parolfactoria  (Brocae), 
which  is  embraced  between  the  anterior  and  posterior  parol- 
factory sulci  and  is  continuous  with  the  area  of  the  same  name 
on  the  base  of  the  cerebral  hemisphere.  This  part  belongs  to 
the  cortical  area  of  smell.  The  posterior  end  of  the  callosal  gyrus 
is  almost  separated  from  the  hippocampal  gyrus  by  the  anterior 
calcarine  fissure ;  the  narrow  link  left  between  this  fissure  and  the 
splenium  of  the  callosum  is  the  isthmus  gyri  fornicati.  It  is 
claimed  by  Schafer  and  others,  that  the  superior  part  of  the  gyrus 
cinguli  constitutes  a  portion  of  the  somaesthetic  area;  but  the 
histological  investigations  of  Dr.  A.  W.  Campbell  appear  to  dis- 
prove such  a  claim.  According  to  Paul  Flechsig,  the  gyrus  cinguh 
contains  the  center  of  taste.  He  locates  the  center  in  the  posterior 
part  of  the  gyrus  adjacent  to  the  splenium  of  the  corpus  callosum; 
it  forms  a  thin  zone  bounding  the  callosal  sulcus  (Fig.  55). 

The  gyrus  hippocampi  (Figs.  26  and  28)  extends  downward 
and  forward,  along  the  hippocampal  fissure,  from  the  isthmus 
to  within  a  half-inch  of  the  temporal  pole.  Its  anterior  extremity 
is  separated  from  the  pole  by  the  ectorhinal  sulcus,  and  is  bent 
upward  and  backward  over  the  end  of  the  hippocampal  fissure, 
forming  a  sharply  curved  hook,  the  uncus.  The  hippocampal 
gyrus  is  bounded  below  and  laterally  by  the  collateral  fissure. 
Posteriorly,  it  is  continuous  with  the  gyrus  linguahs.  The  reflected 
part  of  the  uncus  hippocampi  is  continuous  with  a  concealed 
gyrus,  located  between  the  hippocampal  and  chorioidal  fissures, 
viz.,  the  dentate  fascia;  a  narrow  band,  which  winds  over  the 
uncus  near  its  free  point  and  is  called  the  frenulum  of  Giacomin 
establishes  this  junction  with  the  dentate  fascia. 

The  uncus  and  the  area  parolfactoria  constitute  the  greater 
part  of  the  receptive  center  of  smell  (Figs.  55  and  57).  In  the 
uncus  anterior  to  the  end  of  the  hippocampal  fissure,  Retzius 
locates  the  gyrus  circumambiens  and  gyrus  semilunaris,  which 
he  has  identified  in  the  human  embryo;  and  he  declares  them  to 
contain  the  end  of  the  lateral  olfactory  stria  and  of  the  gyrus 


LOBES  AND  GYRI  OF  MEDIAL  AND  TENTORIAL  SURFACE.   95 


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LOBES  AND  GYRI  OF  MEDIAL  AND  TENTORIAL  SURFACE.   97 

subcallosus,  and  he  thinks  they  form  the  most  imjjortant  jjart 
of  the  receptive  oljaciory  center.  This  region  represents  the 
lobus  pyraformis  of  osmatic  animals  and,  according  to  Elliot 
Smith  (as  quoted  by  Cunningham)  it  is  the  only  part  of  the  gyrus 
hippocampi  which  properly  belongs  to  the  rhinencephalon. 

Limbic  Lobe. — The  parts  of  the  limbic  lobe  may  now  be 
enumerated  as  follows:  (i)  The  gyrus  fornicatus  {g.  cinguli 
and  g.  hippocampi);  (2)  the  fascia  dentata,  fasciola  cinerea, 
supracallosal  gyrus  (longitudinal  striae),  and  subcallosal  gyrus 
(peduncle  of  the  corpus  callosum);  (3)  one-half  of  the  septum 
pellucidum;  and  (4)  a  lateral  half  of  the  fornix.  The  limbic 
lobe  is  rudimentary  in  the  human  brain.  The  structures  enumer- 
ated above  under  No.  2  and  No.  3  are  but  faint  representatives 
of  the  strong  dentate  gyrus  seen  in  animals  having  no  corpus 
callosum.  The  development  of  the  corpus  callosum  encroaches 
upon  and  partially  destroys  the  dentate  gyrus.  The  limbic  lobe 
in  part  belongs  to  the  rhinencephalon.  According  to  the  re- 
searches of  Elliot  Smith  the  posterior  inferior  part  of  the  gyrus 
hippocampi,  that  part  behind  the  uncus  and  below  the  subiculum, 
and  the  whole  gyrus  cinguli  belong  to  the  neopallium  and  not  to 
the  rhinencephalon. 

The  peripheral  ring  on  the  medial  and  tentorial  surface  of 
the  cerebral  hemisphere  is  composed  of  five  gyri  (Figs.  28  and  26). 
Beginning  under  the  corpus  callosum  anterior  to  the  area  parol- 
factoria  and  going  forward  to  the  frontal  pole,  then  along  the 
supero-medial  border  to  the  occipital  pole  and,  finally,  along  the 
infero-lateral  border  to  the  temporal  pole,  these  gyri  are  as  follows : 
The  gyrus  rectus  and  gyrus  frontalis  superior  (g.  marginalis) 
ending  behind  as  lobulus  paracentralis  which  closes  the  superior 
end  of  the  central  sulcus;  the  praecuneus  inclosed  between  the 
marginal  end  of  the  sulcus  cinguli  and  the  sulcus  occipito-pariet- 
alis;  the  cuneus,  located  between  the  occipito-parietal  sulcus 
and  the  posterior  calcarine  fissure;  the  gyrus  lingualis,  which 
forms  much  of  the  medial  occipital  border  and  lies  between  the 
calcarine  and  collateral  fissures;  and  lastly,  the  gyrus  jusijormis 
(temporo-occipital  gyrus),  which  lies  below  the  collateral  fissure 
and  extends  from  the  temporal  pole  almost  to  the  occipital  pole, 
7 


98 


THE    CEREBRUM. 


being  separated  from  the  inferior  temporal  gyrus  by  an  inter- 
rupted sulcus  near  the  infero-lateral  border  of  the  hemisphere. 
The  inferior  temporal  gyrus  is  chiefly  on  the  -convex  surface. 

The  paracentral  lobule  contains  the  motor  center  for  the  opposite 
foot,  just  in  front  of  the  central  sulcus;  and  immediately  behind 
that  sulcus  is  the  superior  part  of  the  receptive  som(Esthetic  area 
(Figs.  55  and  57).  In  the  praecuneus  is  a  part  of  the  stereo  gnostic 
center;  the  remainder  is  in' the  superior  parietal  lobule;  this  center 
belongs  to  the  psychic-sensory  area.  The  cuneus  and  lingual 
gyrus,  along  the  calcarine  fissure  of  each  hemisphere  constitute  the 
receptive  visual  center  for  the  corresponding  halves  of  both  retinae 
and  perhaps  for  both  maculae  luteae.  Probably  the  anterior  part 
of  the  fusiform  gyrus,  that  part  just  below  the  uncus,  contains  the 
center  of  taste  (Mills). 

The  peripheral  ring  of  gyri  seen  on  this  surface  belongs  to  lobes 
which  have  their  largest  exposure  on  the  convex  surface  of  the 
cerebral  hemisphere.  Thus  seven  lobes  belong  to  the  exterior 
surface  of  each  hemisphere. 


Cerebral  Hemisphere  -{ 


Seven  lobes 
Frontal 
Parietal 
Temporal 
Occipital 
Island  (of  Reil) 
Limbic 
Olfactory,  etc. 


2.  Basal  ganglion 


f      I.  Neopallium 


II.  Rhinencephalon 

(archipallium) 
III.  Corpus  striatum. 


INTERIOR  SURFACE  OF  THE  FORE-BRAIN. 

The  boundaries  of  the  fore-brain  ventricles  constitute  the 
interior  surface.  Considering  these  cavities  together,  we  notice 
that  they  occupy  a  wedge-like  space  (Figs.  30  and  42).  In  shape 
the  wedge  is  rectangular;  and  it  stands,  base  upward,  against  the 
corpus  callosum.  Its  beveled  surfaces  look  toward  the  hem- 
ispheres. The  blade  is  driven  downward  as  if  to  split  the  fore- 
brain  into  lateral  halves,  the  edge  resting  on  the  medial  structures 
at  the  base  of  the  brain.     The  space  is  inclosed  laterally  between 


INTERIOR   SURFACE    OF    THE    FORE-BRAIX.  99 

the  di\-erging  internal  capsules,  which,  within  the  hemispheres, 
decussate  with  the  lateral  extremities  of  the  corpus  callosum. 
The  two  structures  most  necessary  to  an  understanding  of  the 
cavities  and  interior  surface  of  the  fore-brain,  therefore,  are  the 
internal  capsule  and  the  corpus  callosum. 

Internal  Capsule.  (Capsula  Interna). — ^Looking  at  the  base 
of  the  brain,  we  see  two  broad  bands  of  nerve  fibers,  the  bases 
pedunculi,  issue  from  the  cerebral  hemispheres  under  cover  of 
the  optic  tracts  and,  converging  do\\Tiward  and  backward,  dis- 
appear in  the  pons  (Figs.  21  and  45).  Traced  in  their  reverse 
direction,  the  fibers  of  each  basis  pedunculi  enter  the  hemisphere 
of  the  cerebrum  and  are  reinforced  by  a  great  number  of  addi- 
tional fibers  from  the  thalamus.  The  fibers  then  radiate  toward 
the  cerebral  cortex  in  the  form  of  a  hollow  cone  or  funnel.  TJiis 
funnel-like  group  of  fibers  is  the  internal  capsule  (Fig.  ^t,).  The 
bell  of  the  funnel  opens  upward  and  outward  and  contains  the 
lentiform  nucleus;  its  solid  spout,  directed  toward  the  pons  and 
medially,  is  the  basis  pedunculi.  Antero-inferiorly  the  fibers 
in  the  bell  of  the  funnel  diverge  to  opposite  sides  of  the  fissura 
cerebri  lateralis  (Syhdi)  and  produce  a  break  in  its  continuity, 
the  hiatus  Syhii;  otherwise  the  funnel  is  complete.  As  the  inter- 
nal capsule  proceeds  into  the  hemisphere,  it  impales  the  corpus 
striatum  in  such  manner  as  to  place  the  caudate  nucleus  upon  its 
circumference  and  to  inclose  within  its  walls  (to  capsulate)  the 
lentiform  nucleus.  The  lentiform  nucleus  is  separated  externally 
from  the  claustrum  by  a  thin  layer  of  fibers  called  the  external 
capsule. 

The  internal  capsule  is  directed  obliquely  outward  and  upward 
and  is  flattened  from  above  dou'n\A-ard.  It  has,  therefore,  a 
superior  and  an  inferior  lamina,  wliich,  posteriorly,  are  continuous 
wdth  each  other  but,  anteriorly,  are  separated  by  the  hiatus  Syhii. 

The  inferior  lamina  (or  inferior  ramus,  as  seen  in  sagittal 
section)  is  thick  behind  but  bevels  down  to  a  sharp  edge  anteriorly 
(Figs.  32,  7,;^,  and  70).  In  front  it  presents  a  free  border.  Its 
fibers  pass  outward  beneath  the  lentiform  nucleus  and,  after 
winding  over  the  inferior  horn  of  the  lateral  ventricle,  terminate 
in  the  parietal,  the  insular  and  temporal  lobes. 


lOO  THE    CEREBRUM. 

Motor  Fibers. — ^The  inferior  lamina  of  the  internal  capsule 
contains  most  of  the  temporo-pontal  tract  itractus  cerehro- 
cortico-pontalis  temporalis)  ^^'hich  extends  from  the  temporal 
cortex  beneath  and  behind  the  lentiform  nucleus  to  the  nucleus 
of  the  pons  and  nuclei  of  the  motor  cerebral  ner^-es.  The  inter- 
mediate tract  {tractus  intermedins)  rises  in  the  lentiform  nucleus 
and  runs  through  the  anterior  part  of  the  inferior  lamina,  in  its 
course  to  the  substantia  nigra  and  nucleus  pontis  in  which  it 
terminates. 

Sensory  Fibers  (Figs.  32,  33  and  70). — ^The  following  sensor}^ 
fibers  are  found  in  the  inferior  lamina,  \iz.,  the  ventral  stalk 
(ansa  peduncularis)  of  the  thalamus  (common  sensor}^)  running 
from  the  thalamus  chiefly  to  the  somaesthetic  cortex;  and  part 
of  the  acustic  or  temporo-thalamic  radiation  (special  sensor}^), 
which  extends  from  the  medial  geniculate  body  to  the  auditory 
cortex  in  the  superior  and  transverse  temporal  gyri.  In  part  at 
least  the  ventral  stalk  rises  from  nuclei  lower  down  than  the  thal- 
amus— from  the  substantia  nigra  and  the  nuclei  of  the  gracile 
and  cuneate  columns  probably.  The  fibers  of  the  ventral  stalk 
of  the  thalamus  are  separated  into  an  upper  and  a  lower  lamina 
by  a  thin  sheet  of  gray  substance.  The  lower  lamina  (inferior 
peduncle  of  the  thalamus)  runs  for  the  most  part  beneath  the 
lentiform  nucleus  into  the  external  capsule  and  terminates  in  the 
temporal  lobe  and  the  island.  The  upper  lamina  (ansa  lenticu- 
laris)  enters  the  lentiform  nucleus  in  two  vertical  sheets  that  separate 
the  three  zones  of  that  nucleus.  Its  fibers  to  a  large  extent  ter- 
minate in  the  lentiform  nucleus,  whose  axones  continue  the  path 
through  the  parietal  stalk,  in  the  superior  lamina  of  the  capsule, 
to  the  somaesthetic  area  of  the  cortex.  In  the  angle  between  the 
inferior  horn  and  the  central  part  of  the  lateral  ventricle,  the 
inferior  lamina  joins  the  superior. 

The  superior  lamina  (or  superior  ramus)  of  the  internal 
capsule  contains  most  of  the  basis  peduncuh  (Fig.  30).  It  is  a 
thick  and  strong  sheet  of  fibers.  Often  it  is  considered  as  the 
entire  "internal  capsule,"  the  inferior  lamina  being  disregarded. 
The  superior  lamina  extends,  fan-like,  from  the  basis  pedunculi  to 
the  lateral  extremity  of  the  corpus  callosum,  wth  which  it  inter- 


INTERIOR    SURFACE    OF    THE    FORE-BRAIN. 


lOI 


Fig.  30. — Transverse  section  of  the  brain,  directed  from  the  pons  obliquely  upward  and 
forward,  showing  internal  capsule,  corpus  callosum,  ganglia  and  ventricles  of  the  fore- 
brain.      (Original.) 

a.  Callosal  sulcus,  bb.  Chorioidal  fissure,  c.  Hippocampal  fissure,  d.  Collateral  fissure,  ee.  Inferior 
horn  of  lateral  ventricle,  f.  Third  ventricle,  g.  Fossa  interpenduncularis.  h.  Caudate  nucleus,  hh.  Cauda. 
i.  Stria  terminalis.  j.  Body  of  fornix,  jj.  Crus  of  fornix,  k.  Red  nucleus.  1.  Hypothalamic  nucleus. 
m.  Substantia  nigra,     o.  Hippocampus,     p.  Dentate  fascia,    r.  Claustrum. 


INTERIOR    SURFACE    OF   THE    FORE-BRAIN.  103 

crosses.  It  has  a  free  border  anteriorly,  though  imbedded  in  the 
corpus  striatum  (Fig.  32).  Upon  its  medial  surface  rest  the 
thalamus,  below  and  behind,  and  the  caudate  nucleus,  above  and 
farther  forward.  It  thus  separates  the  thalamus  and  caudate 
nucleus  from  the  lentiform  nucleus.  A  bend  seen  in  horizontal 
section  near  the  middle  of  the  superior  lamina,  called  the  genu, 
divides  it  into  a  frontal  part  {pars  jrontalis)  and  an  occipital 
part  [pars  occipitalis)  which  tend  slightly  outward  from  the  genu 
and  form  an  angle  with  each  other  of  about  120  degrees. 

Motor  Fibers  of  Superior  Lamina  (Figs.  32,  33  and  70). — 
The  fibers  of  the  genu  and  anterior  two-thirds  of  the  occipital 
part  of  the  internal  capsule  are  very  largely  motor  and  constitute 
the  pyramidal  tract.  They  may  be  traced  from  the  motor  area 
of  the  cortex  (Figs.  54  and  56)  through  the  internal  capsule  and 
the  middle  three-fifths  of  the  basis  pedunculi,  and  on  down  into 
the  spinal  cord.  They  end  in  ramifications  about  the  cell-bodies 
in  the  gray  matter  of  the  cord  and  in  the  motor  cerebral  nuclei. 
From  these  same  spinal  and  cerebral  nuclei  other  fibers  rise  which 
constitute  the  motor  part  of  the  spinal  and  cerebral  nerves.  The 
pars  frontalis  of  the  internal  capsule  contains  a  motor  tract  which 
extends  from  the  frontal  cortex  through  the  inner  one-fifth  of  the 
basis  pedunculi  to  the  nucleus  of  the  pons  and  motor  nuclei  of 
the  cerebral  nerves  (Flechsig).  It  is  the  fronto-pontal  tract 
{tr actus  cerebrO'Cortico- pontalis  frontalis). 

Sensory  Fibers  of  Superior  Lamina  (Figs.  32,  2)2,  and  70). — 
In  both  parts  of  the  superior  lamina  of  the  capsule  there  are 
common  sensory  fibers  which  rise  chiefly  in  the  thalamus  and  end 
in  the  somaesthetic  cortex  (Figs.  54  and  56).  They  convey  ordi- 
nary sensations.  In  the  frontal  part  is  the  frontal  stalk  of  the 
thalamus,  which  ends  chiefly  in  the  caudate  and  lentiform  nuclei, 
though  some  of  its  fibers  reach  the  frontal  cortex.  The  tract  is 
relayed  in  the  lentiform  nucleus,  whence  it  is  continued  to  the 
somaesthetic  cortex  by  way  of  the  parietal  stalk,  which  is  entered 
high  up  near  the  corpus  callosum.  The  pars  occipitalis  of  the 
superior  lamina  contains  the  parietal  stalk  of  the  thalamus, 
which  conveys  ordinary  sensations  from  the  thalamus  to  the  somaes- 
thetic cortex,  chiefly  to  the  posterior  central  gyrus. 


I04  THE    CEREBRUM. 

In  the  extreme  upper  part  of  the  capsule  the  region  of  the 
parietal  stalk  contains  nearly  all  of  the  common  sensory  fibers. 
The  recent  investigations  of  Paul  Flechsig  show  that  it  is  built 
up  of  six  bundles  of  fibers,  two  of  which  (alpha  and  gamma) 
proceed  from  the  globus  pallidus  and  four  from  the  thalamus. 
According  to  Flechsig  there  are  corticifugal  fibers  intermingled 
with  the  corticipetal  in  all  of  the  sensory  tracts  of  the  capsule. 
The  common  sensory  fibers  of  the  internal  capsule  constitute 
the  cortical  fillet. 

Special  Sense  Fibers  (Figs.  32,  33  and  70). — ^At  the  junction 
of  the  superior  and  inferior  laminae  of  the  internal  capsule  are 
the  special  sense  fibers.  The  optic  radiation  (radiatio  occipito- 
thalamica)  and  acustic  radiation  [radiatio  temporo-thalamica) 
occupy  the  retro-lentiform  part  of  the  internal  capsule.  The 
former  extends  through  it  from  the  lateral  geniculate  body  and 
thalamus  to  the  cuneus  and  lingual  gyrus;  the  latter  rises  in  the 
medial  geniculate  body  and  ends  in  the  superior  and  transverse 
tem.poral  gyri.  The  optic  and  acustic  radiations  both  contain 
corticifugal  fibers  which  rise  in  the  visual  and  auditory  cortex, 
respectively,  and  run  through  the  capsule  to  the  lateral  and  medial 
geniculate  bodies  and  perhaps  on  to  lower  nuclei. 

Many  fibers  of  the  internal  capsule  give  off  branches  (collaterals) 
which  pass  through  the  corpus  callosum  to  the  opposite  hemisphere ; 
other  fibers  may  be  traced  entire  through  the  same  course  to  the 
cortical  cells  of  the  opposite  side.  A  bundle  of  thalamic  fibers 
has  been  so  traced. 

The  superior  lamina  of  the  internal  capsule,  proceeding  outward 
and  upward  into  the  hemisphere,  intermingles  with  the  corpus 
callosum  and  enters  into  the  corona  radiata.  Together  with 
the  caudate  nucleus,  thalamus  and  stria  terminalis  (taenia  semi- 
circularis),  which  lie  on  its  medial  surface,  it  forms  the  entire 
lateral  boundary  of  the  general  cavity  of  the  fore-brain.  It  thus 
determines  the  lateral  part  of  the  interior  surface. 

Corpus  Callosum  (Figs.  29,  30,  34  and  42). — ^The  entire  roof 
of  the  fore-brain  cavity,  representing  the  base  of  the  wedge,  is 
formed  by  the  corpus  callosum.  A  part  of  the  anterior  boundary 
is  also  formed  by  it.     The  corpus  callosum  is  a  thick  sheet  of 


INTERIOR    SURFACE    OF    THE    FORE-BRAIN. 


lO! 


C  — ;        C  F 


D.  Ji 


INTERIOR    SURFACE    OF    THE    FORE- BRAIN.  I07 

fibers  four  and  a  half  inches  broad,  from  before  backward ,  which 
joins  the  hemispheres  together.  It  constitutes  the  great  com- 
missure, being  composed  chiefly  of  those  medullated  cortical 
axones  which  end  in  arborizations  about  cortical  cells  of  the 
opposite  hemisphere.  It  contains  some  fibers  which  belong  to 
the  internal  capsule;  and,  also,  collaterals  from  capsular  and 
association  fibers.  The  corpus  callosum  is  placed  nearer  to  the 
anterior  than  the  posterior  pole  of  the  hemispheres.  Separating 
the  hemispheres  above,  it  is  seen  in  the  bottom  of  the  longitudinal 
fissure.     It  is  about  an  inch  in  transverse  length. 

The  upper  surface  is  concave  from  side  to  side,  and  di\ided 
in  the  median  line  by  a  longitudinal  raphe  (Figs.  30  and  34). 
Transverse  striae  are  plainly  visible.  Two  longitudinal  striae 
are  also  found  running  on  either  side  of  the  raphe;  one  next  the 
raphe,  the  medial  longitudinal  stria;  and  the  other  near  the  lateral 
end  of  the  callosum,  the  lateral  longitudinal  stria.  The  medial 
and  lateral  longitudinal  striae  are  imbedded  in  a  thin  sheet  of  gray 
substance  spread  over  the  corpus  callosum;  altogether  they  con- 
stitute the  gyrus  supracallosus.  If  traced  around  the  posterior 
border  of  the  callosum,  this  supracallosal  gyrus  is  found  to  be 
continuous  with  the  fasciola  cinerea  and,  through  that,  with  the 
fascia  dentata.  The  gyrus  supracallosus  becomes  the  gyrus  sub- 
callosus  {peduncle  of  corpus  callosum)  after  it  winds  around  the 
anterior  border  of  the  corpus  callosum.  As  such  it  is  continued 
downward  between  the  lamina  terminalis  and  the  posterior  parol- 
factory sulcus  to  the  base  of  the  cerebrum,  and  then  across  the 
anterior  perforated  substance  to  the  uncus.  At  the  anterior  and 
at  the  posterior  border,  the  corpus  callosum  is  bent  do^^•nward 
(scroll- like) ;  hence,  it  is  superiorly  convex  from  before  back- 
ward. 

Its  inferior  surface  (Figs.  29  and  30)  is  concave  antcro-poste- 
riorly  and  near  its  posterior  border  is  fused  with  the  body  of  the 
fornix.  Anterior  to  that  fusion,  it  is  joined  to  the  fornix,  along 
the  median  line,  by  the  septum  pellucidum. 

The  posterior  border  (Fig.  29)  is  flexed  downward  from  the 
horizontal  about  forty-five  degress.  Giving  passage  to  the  fibers 
which  join  the  middle  and  posterior  parts  of  the  hemispheres, 


Io8  THE    CEREBRUM. 

the  posterior  border  is  the  thickest  part  of  the  corpus  callosum. 
It  is  on  that  account  called  the  pad,  or  splenium. 

The  anterior  border  is  bent  downward  and  then  backward, 
sweeping  through  i8o  degrees  of  flexion  (Fig.  29).  It  tapers 
down  to  a  sharp  edge,  called  the  rostrum.  A  very  thin  sheet-like 
extension  of  the  rostrum,  called  the  lamina  rostralis,  proceeds 
backward  from  the  beak  and  becomes  continuous  with  the  lamina . 
terminalis  at  the  base  of  the  brain.  Running  downward  on  either 
side  is  a  low  ridge,  continuous  with  the  striee  longitudinales, 
which  constitutes  the  gyrus  subcallosus.  Each  gyrus  subcallosus, 
after  passing  across  the  anterior  perforated  substance,  ends  in 
the  uncus  of  the  hippocampal  gyrus.  The  transverse  fibers  of 
the  rostrum,  in  the  hemisphere,  form  the  floor  of  the  anterior  horn 
of  the  lateral  ventricle. 

Genu  and  Truncus  (Fig.  29). — ^The  down-turned  anterior  part 
of  the  corpus  callosum  is  the  genu.  It  joins  the  rostrum  to  the 
main  body,  the  truncus.  The  genu  forms  part  of  the  anterior 
boundary  of  the  cerebral  cavity;  the  truncus  forms  the  roof. 
Fibers  uniting  the  frontal  lobes  of  the  cerebrum  pass  through  the 
genu,  and  in  the  hemisphere,  bound  the  anterior  horn  of  the 
lateral  ventricle  above  and  in  front.  Those  fibers  arching  for- 
ward and  forming  the  roof  of  the  anterior  horn  are  called  the 
forceps  minor.  The  forceps  major,  composed  of  fibers  from  the 
splenium  which  bend  backward  into  the  occipital  lobe,  lies  in  the 
roof  and  inner  wall  of  the  posterior  horn  and  produces  the  eminence 
called  the  bulb  (Fig,  38). 

Each  lateral  extremity  of  the  corpus  callosum  is  overhung  by 
the  gyrus  cinguH,  which  covers  the  lateral  longitudinal  stria. 
Inclosed  between  the  gyrus  cinguli  and  corpus  callosum  is  the 
callosal  fissure  (ventricle  of  the  callosum).  The  lateral  extremity 
of  the  corpus  callosum,  within  the  cerebral  hemisphere,  inter- 
mingles with  the  superior  lamina  of  the  internal  capsule  and 
thus  stretches  entirely  across  the  fore-brain  cavities  (Figs.  30 
and  42). 

The  boundaries  of  the  general  cavity  of  the  fore-brain  may  be 
given  as  follows: 
Roof  (base  of  wedge) — 


INTERIOR    SURFACE    OF    THE    FORE-BRAIN,  1 09 

Corpus  callosum. 
Floor  (edge  of  wedge) — 

Tegmenta  of  mid-brain, 

Posterior  perforated  substance  of  mid-brain, 

Tuber  cinereum, 

Infundibulum, 

Optic  chiasma. 
Lateral  wall  (beveled  surface) — 

Internal  capsule   (superior  lamina), 

Caudate  nucleus, 

Stria  terminalis, 

Thalamus. 
Anterior  wall  (border  of  wedge) — 

Lamina  terminalis, 

Anterior  commissure. 

Genu  of  corpus  callosum. 
Posterior  wall — 

Posterior  commissure  with  cerebral  aqueduct  beneath  it, 

Corpora  quadrigemina  of  mid-brain. 

Pineal  body, 

Transverse  fissure  of  cerebrum,   containing  the  chorioid   tela 
of  third  ventricle, 

Splenium  of  corpus  callosum. 

The  fore-brain  cavity  thus  bounded  is  subdivided  by  two 
partitions  (Figs.  29,  35  and  42).  The  body  of  the  fornix,  together 
with  the  chorioid  tela  of  the  third  ventricle  and  the  roof  epithelium 
of  the  third  ventricle,  forms  a  horizontal  partiiion  which  di\ides 
the  cavity  into  an  upper  and  lower  chamber.  The  sujjcrior 
chamber  is  divided  into  two  lateral  chambers,  the  lateral  ventricles, 
by  a  double  vertical  partition,  the  septum  pellucidum.  The  infe- 
rior chamber  is   the   third  ventricle 

The  body  of  the  fornix  {corpus  fomicis,  Figs.  29  and  36)  is 
a  triangular  sheet  of  fibers,  whose  base  is  attached  to  the  under 
surface  of  the  splenium  of  the  corpus  callosum,  and  whose  l)ilKl 
apex  extends  forward  to  the  rostrum  and  the  anterior  com- 
missure. Its  lateral  borders  rest  on  the  thalami,  the  chorioid 
tela  alone  intervening  (Fig.  42).    And  the  narrow  chamber  between 


no  THE    CEREBRUM. 

the  thalami,  the  third  ventricle,  is  separated  from  the  broader, 
superior  part  of  the  fore-brain  cavity  by  the  body  of  the  fornix 
together  with  the  chorioid  tela  and  a  layer  of  epithelium.  The 
body  of  the  fornix  is  produced  by  the  approximation  of  two 
bundles  of  white  fibers,  one  belonging  to  each  hemisphere.  These 
bundles  are  the  crura  of  the  fornix. 

The  crus  fornicis  (Figs.  29,  38  and  39)  may  be  traced  from 
the  uncus  and  the  hippocampus,  its  chief  origin,  upward  through 
the  inferior  horn  and  into  the  floor  of  the  body  of  the  lateral  ven- 
tricle, where  it  unites  with  its  fellow  of  the  opposite  side  in  forming 
the  body  of  the  fornix.  At  the  apex  of  the  body  of  the  fornix, 
which  is  the  anterior  end,  the  bundles  again  separate  and  become 
the  columnae  of  the  fornix.  The  crura  are  united  at  the  back 
part  of  the  body  of  the  fornix  by  a  few  transverse  and  oblique 
fibers  which  form  the  lyre,  or  commissura  hippocampi  (Fig.  36). 
The  commissure  is  best  seen  when  the  corpus  callosum  and  fornix 
are  viewed  from  below;  its  fibers  connect  each  crus  of  the  fornix 
with  the  hippocampus  and  uncus  of  the  opposite  side. 

The  eolumnae  fornicis  (Figs.  29  and  40),  one  on  either  side 
pass  down  in  front  of  the  thalami,  bounding  the  foramina  inter- 
ventricularia  (Monroi);  and  then  descend  to  the  corpora  mammil- 
laria,  at  the  base  of  the  brain.  On  the  way  down,  each  columna 
{pars  libera)  passes  behind  the  anterior  commissure,  beyond 
which  (pars  tecta)  it  pierces  the  inner  part  of  the  thalamus  of  the 
same  side.  The  fibers  of  the  columna  fornicis  for  the  most  part 
terminate  in  the  medial  nucleus  of  the  corpus  mammillare,  from 
which  other  fibers  take  their  origin,  forming  the  fasciculus  mam- 
miUaris  princeps.  This  bundle  divides  Y-like;  the  anterior 
branch  is  the  fasciculus  thalamo-mammillaris  (Vicq  d'Azyri) 
and  ascends  to  the  anterior  nucleus  of  the  thalamus;  the  posterior 
bundle  is  the  tegmental  part  of  the  fasciculus  pedunculo-mam- 
millarls  and  probably  ends  in  the  stratum  griseum  centrale  of 
the  mid-brain. 

At  the  lower  border  of  the  interventricular  foramen  a  small 
bundle  of  fibers  leaves  the  columna  of  the  fornix  and,  bending 
backward,  runs  as  medullary  stria  along  the  thalamus  to  the 
nucleus  of  the  habenula;  some  of  the  fibers  decussate  through 


THE    FIFTH    VENTRICLE.  Ill 

the  stalk  of  the  jiincal  body  to  the  opposite  nucleus  habenuhe 
and  constitute  the  conimissura  habenularum.  The  columna 
of  the  fornix  is  joined  by  a  small  fasciculus  from  the  medial  root 
of  the  olfactory  tract,  which  runs  backward  to  the  hippocampus 
and  uncus. 

The  upper  surface  of  the  body  of  the  fornix  is  convex  from 
before  backward  (Figs.  29  and  36).  It  forms  the  postero-medial 
part  of  the  floor  of  the  lateral  ventricle.  Along  the  median  line, 
it  is  joined  to  the  corpus  callosum  by  the  septum  pellucidum. 

The  septum  pellucidum  (Figs.  29,  35,  40  and  73),  a  double- 
walled  median  partition,  divides  the  superior  chamber  of  the 
fore-brain  cavity  into  lateral  halves,  the  lateral  ventricles.  The 
septum  pellucidum  is  crescentic  in  outline.  Its  convex  border 
fits  into  the  concave  surface  of  the  body,  genu  and  rostrum  of  the 
corpus  callosum.  Its  concave  border  rests  upon  the  fornix. 
Between  the  rostrum  of  the  corpus  callosum  and  the  anterior 
commissure,  the  septum  pellucidum  is  continuous  with  the  gyrus 
subcallosus  with  which  it  is  associated  in  development  and  func- 
tion. 

The  septum  pellucidum,  like  the  anterior  commissure,  corpus 
callosum  and  fornix,  is  developed  from  the  thickened  upper  border 
of  the  lamina  terminalis  and  the  adjacent  medial  wall  of  the 
cerebral  hemisphere  in  front  of  the  interventicular  foramen. 
These  several  structures  extend  upward  and  backward  with  the 
development  and  rotation  of  the  hemispheres  and,  together, 
roof  over  the  inter- brain.  A  lymph  space,  the  cavum  septi  pellucidi, 
appears  in  the  septum  and  is  commonly  called  the  ^jth  ventricle. 
The  fore-brain  cavity  thus  embraces  four  ventricles,  viz.: 

Two  lateral  ventricles  (the  ventricles  of  the  hemispheres). 

Fifth  ventricle  (the  ventricle  of  the  septum),  and 

Third  ventricle  (ventricle  of  the  inter-brain). 

THE  FIFTH  VENTRICLE. 

'    {Cavum  Septi  Pellucidi.) 

This  is  the  ventricle  of  the  septum  (Figs.  35  and  73).  The 
fifth  ventricle  is  a  very  narrow,  antero-posterior  cleft  between 
the  walls  of  the  septum  pellucidum,  with  which  it  coincides  in 


112  THE    CEREBRUM. 

extent.  It  is  situated  within  the  concavity  of  the  corpus  callo- 
sum  between  the  lateral  ventricles,  above  and  anterior  to  the 
third  ventricle.  Below  and  posteriorly  it  is  bounded  by  the  fornix. 
It  is  not  a  part  of  the  embryonic  brain  cavity,  but  a  mere  lymph 
space.  Therefore  it  does  not  communicate  with  any  other 
ventricle,  each  of  the  others  being  a  part  of  the  cavity  of  the 
neural  tube  from  which  both  brain  and  cord  are  developed. 
Instead  of  ependyma,  which  lines  other  ventricles,  the  lining  of 
the  fifth  is  endothelium.     A  lymph-like  fluid  fills  it. 

THE  LATERAL  VENTRICLE. 

( Ventriciilus  Lateralis. ) 

The  hemispheres  contain  the  largest  of  the  six  ventricles  (Figs. 
30,  35,  41,  42  and  73).  Situated  one  on  either  side  of  the  median 
line,  the  ventricles  of  the  hemispheres  are  very  naturally  called 
the  lateral  ventricles.  Each  represents  a  branch  of  the  cavity 
of  the  embryonic  neural  tube  (Figs.  17  and  41).  In  consequence, 
the  lateral  ventricles  communicate  with  all  others  except  the 
fifth.  By  the  interventricular  foramen  (of  Monro),  each  directly 
communicates  with  the  third  ventricle;  and  through  that,  indirectly, 
with  the  fourth  and  sixth.  The  foramen  interventriculare  is 
situated  between  the  front  of  the  thalamus  and  the  calumna  of 
the  fornix  (Fig.  29).  It  extends  between  the  anterior  extremity 
of  the  third  ventricle  (the  aula)  and  the  junction  of  the  anterior 
horn  with  the  central  part  of  the  lateral  ventricle.  The  lateral 
ventricles  are  lined  with  ependyma,  which  is  a  transparent  mem- 
brane composed  of  two  layers  when  complete,  viz.,  neuroglia 
and  a  covering  of  columnar  ciliated  epithelial  cells.  Over  the 
thalamus  (the  part  seen  in  the  lateral  ventricle)  and  the  chorioid 
plexus,  the  neurogliar  layer  is  absent. 

The  lateral  ventricle  may  be  studied  best  in  four  parts:  the 
central  part  (or  body);  the  anterior  horn;  the  inferior  horn;  and 
the  posterior  horn. 

The  central  part  of  the  lateral  ventricle  (Figs.  36,  39  and  40) 
is  the  ventricle  of  the  parietal  lobe  of  the  cerebrum.  The  following 
are   its    boundaries : 

Roof — Corpus  callosum. 


THE    LATERAL    VENTRICLE. 


"3 


-^^.^-^-A 


THE    LATERAL    VENTRICLE.  II5 

Floor   (from  before,  backward  and  inward) — 

Caudate  nucleus  of  the  corpus  striatum, 

Stria  terminalis  (taenia  semicircularis), 

Thalamus  (covered  by  epithelium), 

Lamina  chorioidea  epithelialis  and  chorioid  plexus, 

Fornix. 
Medial  wall — Septum  pcllucidum. 
External  wall — Internal  capsule. 

The  corpus  callosum  forms  a  complete  roof  for  the  central  part 
of  the  lateral  ventricle.  The  roof  inclines  upward  and  outward 
from  the  septum  pellucidum,  the  inner  wall  of  the  ventricle,  to 


Fig-  ?)i- — Diagram  of  internal  capsule  in  colors.     {Original.) 
Red,  motor;  blue,  common  sensor)-;  purple,  special  sensor^-. 

the  superior  lamina  of  the  internal  capsule,  which  forms  its  outer 
wall.  The  floor  of  the  central  part  of  the  ventricle  is  formed  by 
the  five  parts,  as  named  abo^•e,  which  will  now  be  considered 
in  the  order  given.  '' 

Corpus  Striatum  (Figs.  30,  31,  32  and  40). — The  striated  body 
is  the  basal  ganglion  of  the  hemisphere.  It  is  an  ovoid  mass  of 
gray  matter  imbedded,  for  the  most  part,  in  the  cerebral  medulla; 
but  it  is  continuous  below  with  the  anterior  perforated  substance, 
and  extends  above  to  the  lateral  ventricle.  It  measures  two 
and  a  half  inches  from  before  backward,  an  inch  and  a  quarter 


Il6  THE    CEREBRUM, 

transversely,  and,  from  above  downward,  one  inch  and  a  half. 
It  is  placed  anterior  and  external  to  the  thalamus  and  forms 
the  third  of  the  great  divisions  of  the  cerebral  hemisphere,  viz., 
the  neopallium,  the  rhinencephalon  and  the  corpus  striatum.  It 
is  a  reddish-gray  body,  and  its  streaked  appearance  is  due  to  the 
white  capsular  fibers  which  pierce  it.  The  striated  body  is  an 
important  relay  in  the  motor  conduction  path  and  one  of  less 
importance  in  the  sensory  path.  The  internal  capsule  divides 
it  into  two  nuclei,  namely,  the  lentijorm  nucleus  (extraventricular 
part),  and  the  caudate  nucleus,  which  is  seen  in  the  boundary  of 
the  lateral  ventricle.  Anterior  to  the  free  borders  of  the  supe- 
rior and  inferior  capsular  laminae,  the  two  nuclei  are  united  with 
each  other,  with  the  anterior  perforated  substance  and  with  the 
lower  end  of  the  claustrum. 

The  lentiform  nucleus  {nucleus  lentijormis)  occupies  the 
cone-like  cavity  of  the  internal  capsule,  by  whose  laminae  it  is 
separated  from  the  ventricle  (Fig.  32).  It  is  shorter  fore  and 
aft  than  the  caudate  nucleus.  It  resembles  a  biconvex  lens  with 
a  somewhat  thickened  anterior  border,  when  viewed  in  horizontal 
section  (Fig.  31).  In  transverse  vertical  section  through  its 
center,  it  is  triangular  in  shape.  The  hypotenuse  and  base  are 
formed,  respectively,  by  the  superior  and  inferior  laminae  of  the 
internal  capsule.  The  external  capsule  forms  the  pefjpendicular 
and  separates  the  lentiform  nucleus  from  the  claustrum.  The 
latter  is  a  thin  sheet  of  isolated  gray  matter,  found  just  medial  to 
the  island  (of  Reil).  In  extent  and  position,  fore  and  aft,  the 
island  and  lentiform  nucleus  coincide.  The  lentiform  nucleus 
is  subdivided  by  two  white  laminae,  parallel  with  its  external  sur- 
face, into  three  zones.  (Fig.  30).  The  outer  zone,  called  the 
putamen,  is  deeply  pigmented,  and,  like  the  caudate  nucleus,  is  of 
a  reddish-gray  color;  but  the  two  inner  zones,  having  less  pig- 
ment, are  of  a  pale  yellowish  tint.     They  form  the  globus  pallidus. 

The  nucleus  caudatus  (the  tailed  nucleus)  is  a  pear-shaped 
body  of  reddish-gray  color,  situated  on  the  perimeter  of  the  inter- 
nal capsule  (Figs.  30,  32  and  40).  It  is  the  intraventricular 
part  of  the  striated  body  and  forms  a  strip  of  the  ventricular  floor 
along  the  outer  wall.     The  head  {caput)  of  the  caudate  nucleus 


THE    LATERAL    VENTRICLE. 


117 


c^^jr  6^jp^^^^c.  OF 


z>  5  s-\?^  b  '\  A  L    r]  5  i^'j  j^  y  }i  iisiZ^ 


-  ..  '■•■1  i  ■  I  U;i,„ 
.  -  -    ;..;r  '-^  ^<  P  u  Sj 

■^^Teb-     ^  ■ !~  '^  -S   ^j"  fvi     '  "^ 


V'  V. 


Fig.  34. — Dorsal  surface  of  corpus  callosum,  cerebral  hemisphere  cut  away  to 
expose  it.     {Original.) 


THE    LATERAL    VENTRICLE.  IIQ 

is  directed  forward.  It  is  seen  in  the  anterior  horn  of  the  hiteral 
ventricle.  From  the  head  the  nucleus  tapers  as  it  proceeds  back- 
ward through  the  central  part  of  the  ventricle.  Its  tail  (cauda) 
turns  downward  in  the  roof  of  the  inferior  horn,  and  ends  in  a 
considerable  mass  of  gray  substance  called  the  nucleus  amygdala;, 
which  appears  to  be  an  ingrowth  of  cortex  from  the  region  of  the 
uncus  hippocampi  (Fig.  32).  The  caudate  nucleus  is  covered 
on  its  ventricular  surface  by  ependyma.  The  opposite  surface, 
resting  against  the  fibers  of  the  internal  capsule,  is  irregular  and 
serrated. 

The  stria  terminalis  (taenia  semicircularis.  Figs.  30  and  36) 
lies  just  medial  to  the  nucleus  caudatus.  It  is  a  band  of  white 
fibers  traversing  the  floor  of  the  central  part  of  the  ventricle  and 
the  roof  of  its  inferior  horn,  but  covered  by  the  terminal  vein 
and  by  the  ependyma.  It  may  be  said  to  rise  from  the  nucleus 
amygdalae.  Ascending  to  the  ventricle,  it  passes  forward  between 
the  caudate  nucleus  and  the  thalamus  to  the  interventricular 
foramen,  where  it  divides  into  two  bundles.  One  of  them  accom- 
panies the  columna  of  the  fornix  for  a  little  way.  The  other, 
passing  over  the  anterior  commissure,  descends  in  front  of  it;  and, 
according  to  Kolliker,  both  bundles  end  in  the  anterior  perforated 
substance  (Cunningham).  The  thin  medial  border  of  the  sub- 
stance covering  the  vena  terminalis,  which  is  attached  to  the 
thalamus,  is  called  the  lamina  affixa;  it  is  present  only  in  the  body 
of  the  ventricle.  The  lamina  affixa  is  joined  by  a  single  layer  of 
epithelium,  the  lamina  chorioidea  epithelialis,  to  the  lateral  border 
of  the  fornix.  This  lamina  invests  the  chorioid  plexus  of  the 
lateral  ventricle.  If  the  chorioid  epithelium  be  torn  away,  the 
edge  which  remains  on  the  stria  terminalis  is  called  the  tcenia 
terminalis. 

Thalamus  (Figs.  30,  31,  36  and  40).— x\  fusiform  part  of  this 
ganglion  of  the  inter-brain  is  visible  in  the  floor  of  the  lateral 
ventricle,  between  the  stria  terminalis  and  the  chorioid  plexus. 
It  extends  throughout  the  central  part  of  the  ventricle  from  the 
interventricular  foramen  to  the  inferior  horn.  A  transparent 
layer  of  epithelium,  the  lamina  chorioidea  epithelialis,  extending 
from  the  fornix  to  the  stria  terminalis  and  representing  the  hemi- 


120  THE    CEREBRUM. 

sphere  wall,  covers  it.  The  thalamus  will  be  described  with 
the  third  ventricle  and  inter-brain. 

The  chorioid  plexus  {plexus  chorioideus,  Figs.  35,  36  and  37) 
of  the  lateral  ventricle  is  the  vascular  border  of  the  chorioid  tela 
of  the  third  ventricle.  It  projects,  laterally,  from  beneath  the 
fornix  and  its  crus  through  the  chorioidal  fissure  into  the  floor 
of  the  central  part  of  the  ventricle  and  the  inner  wall  of  the  inferior 
horn.  The  epithehum,  above  mentioned,  invests  it;  and  it  borders 
the  fornix  like  a  ruffle.  It  is  called  chorioid  plexus  {chorion, 
a  membrane)  because  it  is  membrane-like.  At  the  junction  of 
the  central  part  and  inferior  horn  of  the  lateral  ventricle  the 
chorioid  plexus  presents  a  large  skein-like  mass  called  the  glomus 
chorioideum  (Fig.  36).  The  anterior  chorioidal  artery  from  the 
internal  carotid  and  the  postero-lateral  chorioidal,  a  branch  of 
the  posterior  cerebral,  supply  the  plexus.  The  former  pierces 
the  temporal  lobe  and  enters  the  apex  of  the  inferior  horn  of  the 
ventricle;  the  latter  passes  in  through  the  transverse  and  chorioidal 
fissures  of  the  cerebrum,  following  the  chorioid  tela.  The  chori- 
oidal vein  carries  the  blood  away.  At  the  foramen  interventricu- 
lare,  it  is  joined  by  the  terminal  vein  of  the  striated  body  and  the 
veins  of  the  septum  pellucidum  and  forms  the  internal  cerebral 
vein.  The  internal  cerebral  vein  courses  backward  in  the  chorioid 
tela  and  unites  with  its  fellow  of  the  opposite  side,  proximal  to 
which  union  it  receives  the  basilar  vein ;  and  then  the  great  cerebral 
vein  (of  Galen),  uniting  vdth  the  inferior  sagittal  sinus,  forms  the 
straight  sinus. 

The  floor  of  the  central  part  of  the  lateral  ventricle  is  com- 
pleted by  the  superior  surface  of  the  fornix. 

The  horns  of  the  lateral  ventricle  are  three  in  number;  the 
anterior,  inferior  and  posterior  (Figs.  39,  40  and  41). 

The  anterior  horn  {cornu  anterius,  Figs.  35,  36  and  73)  projects 
from  the  central  part  of  the  ventricle  forward  and  outward  around 
the  head  of  the  caudate  nucleus.  It  is  the  ventricle  of  the  frontal 
lobe  and  is  deep  and  narrow.     Its  boundaries  are  as  follows: 

Roof — Corpus  callosum  (forceps  minor). 

Floor — Rostrum. 

Anterior  wall — Genu. 


THE    LATERAL    VENTRICLE. 


121 


Fig.  35. — Horizontal  section  of  cerebrum,  cutting  splenium  and  genu  of  corpus 
callosum,  showing  lateral  ventricles,  septum  pellucidum,  fornix  and  transverse 
temporal  gyri.      (Original.) 


THE    LATERAL    VENTRICLE.  1 23 

Inner  wall — Septum  jjcllucidum. 

Outer  wall — Caudate  nucleus. 

The  posterior  horn  [cornu'  poslcrius,  Figs.  35,  36,  38,  39,  40 
and  41)  is  directed  backward  and  downward  in  a  curve  concave 
inward,  from  the  ventricular  center  into  the  occipital  lobe;  and, 
like  the  occipital  lobe,  it  first  makes  its  appearance  in  the  fifth 
month  of  embryonic  life.  Its  extremity  bends  medially  toward 
the  posterior  calcarine  fissure,  with  which  the  horn  is  parallel. 
The  anterior  calcarine  fissure  produces  the  ridge  along  the  inner 
wall  called  the  calcar  avis.  The  posterior  horn  is  roofed  over 
by  fibers  from  the  splenium  of  the  corpus  callosum,  which  turn 
down  outside  the  horn  and  also  form  part  of  the  external  boundary. 
In  the  external  wall  and  in  the  roof  and  floor  is  also  the  optic 
radiation.  A  well-marked  bundle  of  fibers  from  the  splenium, 
forceps  major,  is  found  passing  along  the  medial  border  of  the  roof 
into  the  occipital  lobe.  It  produces  an  eminence  above  flic  calcar 
avis,  called  the  bulb.  The  anterior  extremity  of  the  posterior  horn 
is  continuous,  inferiorly,  with  the  beginning  of  the  inferior  horn.  At 
the  junction  of  the  two  is  a  triangular  area,  the  irigonum  collaterale. 

The  inferior  horn  {cornu  inferius,  Figs.  32,  38,  39  and  41) 
is  the  ventricle  of  the  temporal  lobe.  Its  course  is  crescentic, 
as  it  follows  the  perimeter  of  the  internal  capsule.  It  first  runs 
outward  and  backward  from  the  body  of  the  ventricle,  then  it 
turns  downward,  and  finally  it  proceeds  horizontally  forward 
and  inward  to  within  an  inch  of  the  pole  of  the  temporal  lobe. 
In  horizontal  section  just  below  the  general  cavity  of  the  ventricle, 
the  inferior  horn  is  triangular.  In  that  position  it  has  a  posterior 
wall  (or  floor  in  the  horizontal  part),  a  medial  icall,  and  a  curved 
aniero-lateral  wall  (or  roof  in  the  horizontal  portion)  which  is 
continuous  above  with  the  outer  wall  and  floor  of  the  central 
part  of  the  ventricle. 

The  parts  found  in  the  walls  of  the  inferior  horn  may  be  enumer- 
ated as  follows: 

Roof  (or  antero-lateral  wall) — 

Inferior   lamina   of   internal   capsule,    partially   covered    by 
tail  of  caudate  nucleus,  stria  terminalis  and  amygdala. 

Tapetum   Floor   (or  posterior  wall) — 


124  THE    CEREBRUM, 

Eminentia  collateralis  (trigonum  collaterale), 

Hippocampus, 

Crus  of  fornix. 
Inner  wall   (medial)  — 

Epithelium  (of  hemisphere  wall)  covering 

Pulvinar, 

Chorioid  plexus, 

Chorioidal  fissure,  and 

Dentate  fascia. 
The  structures  in  the  roof  of  the  inferior  horn  have  been  suffi- 
ciently described.  They  are  easily  understood  when  it  is  recalled 
that  the  roof  of  the  horn  is  continuous  with  the  outer  wall  and 
floor  of  the  central  part  of  the  ventricle;  the  tapefum,  the  internal 
capsule  (inferior  lamina),  the  cauda,  amygdala  and  the  stria 
terminalis  form  it. 

Beginning  at  the  trigonum  collaterale  (Figs.  38  and  39)  and 
extending  along  the  outer  border  of  the  floor  to  the  end  of  the 
inferior  horn  there  is  sometimes  a  low  ridge  caused  by  the  collateral 
fissure.  It  is  the  eminentia  collateralis,  and  is  present  only  when 
the  anterior  part  of  the  collateral  fissure,  as  well  as  the  middle 
part,  is  a  complete  fissure.  The  short  eminence  at  the  entrance 
to  the  inferior  Horn,  called  the  trigonum  cohaterale,  is  constant 
in  its  presence;  it  is  produced  by  the  middle  division  of  the  col- 
lateral fissure.  In  front  of  this  eminence  and  internal  to  it  is  a 
prominent  ridge,  the  hippocampus,  which  enlarges  downward  to 
a  lobulated  extremity,  called  the  digitations  (digitationes  hippo- 
campi. Fig.  39).  The  ridge  is  due  to  the  infolding  of  the  floor 
over  the  hippocampal  fissure  on  the  medial  surface  of  the  cere- 
brum. The  ventricular  surface  of  the  hippocampus  is  formed 
by  a  lamina  of  white  matter,  the  alveus,  but  the  deeper  part  is 
cortical  matter  composed  almost  entirely  of  pyramidal  cell-bodies. 
The  crus  of  the  fornix  (fimbria  hippocampi)  rests  in  the  concavity 
of  the  hippocampus,  where  most  of  its  fibers  originate,  though 
a  smah  bundle  of  them  passes  beyond  it  to  its  origin  in  the  uncus. 
The  chorioid  epithelium  (lamina  chorloidea  epithelialis)  (Figs. 
118,  62  and  35),  representing  the  hemisphere  wall,  forms  the 
floor  of  the  chorioidal  fissure  and  the  whole  medial  wall  of  the 


THE    LATERAL    VENTRICLE. 


Fig.  36. — Horizontal  section  of  cerebrum  just  below  splenium  of  corpus  callosum, 
showing  commissura  hippocampi,  fornix,  septum  pellucidum,  the  island  and 
lateral  ventricles.     {Original.) 

S.  C.A.  Sul.  circularis  anterior.     S.  C.  P.  Sul.  circularis  posterior. 


THE    THIRD    VENTRICLE    AND    INTER-BRAIN.  1 27 

inferior  horn.  It  covers  the  cushion-Hke  projection  (the  pulvi- 
nar)  of  the  thalamus,  which  forms  a  small  part  of  both  roof  and 
inner  wall.  Behind,  it  is  attached  to  the  crus  of  the  fornix,  from 
which  it  extends  forward  to  the  stria  terminalis.  The  epitheHum 
covers  the  chorioidal  fissure  except  at  the  lower  part,  where  there 
is  a  small  cleft  which  forms  a  communication  between  the  horn 
and  the  anterior  subarachnoid  space.  Through  the  chorioidal 
fissure  a  fold  of  pia  mater  projects  toward  the  ventricle,  and 
pushing  the  epithelium  before  it  into  the  horn,  forms  the  chorioid 
plexus  (Figs.  35  and  36).  Bounding  this  part  of  the  chorioidal 
fissure  below  and  behind,  there  is  a  serrated  free  border  of  cortex 
called  the  dentate  fascia.  The  dentate  fascia  (Figs.  38,  42  and  62) 
folds  medially  in  front  of  the  hippocampal  fissure  and  with  the 
hippocampus,  the  gyrus  hippocampi  and  the  eminentia  collateralis 
forms  an  S-shaped  fold  of  the  cortex.  The  S-shape  is  perfect 
in  the  left  hemisphere,  when  the  anterior  segment  of  a  coronal 
section  is  viewed  from  behind.  The  top  of  the  letter  is  the  dentate 
fascia;  the  superior  curve  is  the  hippocampus,  produced  by  the 
hippocampal  fissure;  the  lower  convexity  is  the  gyrus  hippo- 
campi; the  lower  concavity,  open  toward  the  ventricle,  is 
the  groove  between  the  hippocampus  and  the  eminentia  col- 
lateralis. 

THE  THIRD  VENTRICLE  AND  INTER-BRAIN. 

(Ventriculus  Tertius  and  Diencephalon.) 

The  inter-brain  {diencephalon)  is  median  in  position  (Figs. 
27,  28,  29,  30  and  40).  It  is  situated  beneath  the  fornix  and  the 
layer  of  epithelium  extending  from  the  border  of  the  fornix  to  the 
stria  terminalis.  The  chorioid  tela  of  the  third  ventricle  only 
intervenes  between  them.  Laterally,  it  is  bounded  by  the  superior 
laminae  of  the  internal  capsules.  The  ventricle  of  the  inter-brain 
is  the  third  in  number.  The  third  ventricle,  therefore,  is  located 
in  the  median  plane;  and  is  at  a  lower  level  than  the  ventricles 
of  the  hemispheres.  Through  the  interventricular  foramina, 
its  anterior  part  (the  aula)  communicates  with  each  lateral  ventri- 
cle, and  the  cerebral  aqueduct  connects  it,  behind,  with  the  fourth 
ventricle  (Figs.  17  and  41).     The  third  \entricle  is  tissure-like. 


128  THE    CEREBRUM. 

It  is  a  narrow,  vertical  cleft  about  an  inch  in  length  from  before 
backward  and  a  quarter  of  an  inch  broad  at  its  widest  part  It 
separates  the  thalami,  and  extends  almost  to  the  inferior  surface 
of  the  cerebrum.  The  roof  (Figs.  29,  36,  37,  40  and  42)  follows  the 
curve  of  the  fornix  and  arches  from  the  posterior  commissure 
forward  to  the  anterior  commissure.  There  is  a  little  recess 
above  the  anterior  commissure  and  between  the  columnae  of  the 
fornix,  bounded  in  front  by  the  inferior  angle  of  the  septum  pel- 
lucidum,  called  the  recessus  triangularis,  in  which  the  roof  and 
anterior  wall  meet.  The  anterior  wall  extends  from  the  trian- 
gular recess  down  to  the  optic  recess,  at  the  angle  between  the 
lamina  cinerea  and  the  optic  chiasma.  This  angle  is  so  named 
because,  on  either  side  of  it,  there  is  a  lateral  extension  of  the 
third  ventricle  between  the  lamina  terminalis  and  the  columna 
of  the  fornix,  which  is  located  in  the  root  of  the  embryonic  optic 
vesicle.  The  floor  (Fig.  28)  describes  two  arches,  convex  toward 
the  ventricle.  The  first  arch,  very  convex  and  short,  stretches 
between  the  optic  recess  and  the  infundibulum,  in  which  the 
floor  reaches  its  lowest  point.  The  distance  from  the  infundib- 
ulum to  the  anterior  orifice  of  the  cerebral  aqueduct  is  spanned 
by  the  second-arch.  It  is  long  and  flat.  Its  posterior  extremity 
is  but  a  sixteenth  of  an  inch  below  the  posterior  commissure;  the 
anterior  orifice  of  the  cerebral  aqueduct  separates  them.  The 
ventricle  is  thus  contracted  behind  to  the  size  of  the  cerebral 
aqueduct,  with  which  it  is  continuous.  The  lateral  walls  (Figs. 
28  and  29)  are  close  together  throughout.  At  one  point  near  the 
middle  they  come  together  and  are  joined  by  the  massa  inter- 
media (middle  commissure).  Antero-superiorly,  the  lateral  wall 
is  perforated  by  the  interventricular  foramen  (of  Monro).  That 
foramen  constitutes  the  slight  separation  between  the  front  of  the 
thalamus  and  the  columna  of  the  fornix.  It  opens  into  the  lateral 
ventricle  at  the  junction  of  the  anterior  horn  with  the  central  part. 
The  ependyma  which  lines  the  third  ventricle  is  continuous  through 
the  interventricular  foramen  with  the  lining  of  the  lateral  ventricle. 
But  one  layer  of  the  ependyma  is  present  in  the  roof  of  the  ven- 
tricle; that  is  the  epithelial  layer.  The  third  ventricle,  like  all 
true  ventricles,  is  occupied  by  cerebro-spinal  fluid. 


THE    THIRD    VENTRICLE    AND    INTER-BRAIN. 


129 


•f^^g-  37- — Horizontal  section  of  cerebrum.     Fornix  turned  back,  showing  chorioid 
tela  of  third  ventricle,  and  internal  cerebral  veins.     {Original.) 


THE    THIRD    VENTRICLE    AND    INTER-BRAIN. 

The  following  are  the  boundaries  of  the  third  ventricle: 

Roof- 
Posterior   commissure   and   commissura   habenularum, 
Roof  epithelium  and  pineal  body, 
Chorioid  tela  and  plexuses, 
Fornix  and  commissura  hippocampi. 


131 


Fig.  38.— Transverse  section  of  left  cerebral  hemisphere  cutting  the  splenium  and 
showing  the  posterior  horn  and  the  floor  of  the  inferior  horn  of  the  lateral 
ventricle.     {Original.) 

a.  Crus  fornicis.  b.  Fis.  hippocampi,  c.  Hippocampus,  d.  Fascia  dentata.  e.  Eminentia 
collateralis.  f.  Fis.  collateralis.  h.  Calcar  avis.  i.  Bulb  caused  by  forceps  major,  j.  Tape- 
tum.     k.  Radiatio  occipito-thalamica.     1.  Fasciculus  longitudinalis  inferior. 

Anterior  wall — 

Epithelium,  covering 

Columnae  of  fornix,  anterior  commissure,  and 
Lamina  teiTninalis. 
Floor — 

Optic  commissure, 

Tuber  cinereum  and  infundibulum, 

Corpora  mammillaria. 


132  THE    CEREBRUM. 

Posterior  perforated  substance  (of  mid-brain), 

Tegmenta  (of  mid-brain). 
Posteriorly — 

Ventricle  is  continuous  with  cerebral  aqueduct. 
Lateral  walls — 

Thalamus,  and  reflected  hypothalamic  substance, 

Columna  of  the  fornix,  and 

Foramen  interventriculare  between  them. 
Roof. — ^A  band  of  white  fibers  passes  across  the  back  part  of 
the  third  ventricle  and  supports  the  posterior  end  of  the  roof 
epithelium.  That  band  is  the  posterior  commissure  {commissura 
posterior,  Figs.  28  and  40).  It  crosses  immediately  in  front  of 
the  corpora  quadrigemina.  Beneath  it  is  the  anterior  orifice  of 
the  cerebral  aqueduct.  The  pineal  body  is  above  and  behind  it, 
and  the  commissure  fuses  with  the  ventral  pineal  lamina.  The 
posterior  commissure  stretches  from  the  central  gray  substance 
of  the  mid-brain  on  one  side,  over  the  aqueduct,  to  the  gray  sub- 
stance of  the  opposite  side  and  also  contains  decussating  fibers 
of  the  medial  longitudinal  bundle  (Heald).  The  commissure 
is  in  need  of  further  investigation. 

The  roof  epithelium  (Figs.  42  and  37)  of  the  third  ventricle 
stretches  from  the  posterior  commissure  to  the  anterior  commissure, 
and  laterally,  is  attached  to  the  upper  internal  border  of  the  thal- 
amus. It  is  the  superficial  layer  of  the  ependyma;  but  it  is,  here, 
the  only  adult  representative  of  the  roof  of  the  diencephalon. 
The  roof  epithelium  presents  two  longitudinal  folds  suspended 
in  the  ventricle.  The  lower  layer  of  the  chorioid  tela  of  the  third 
ventricle,  invests  the  roof  epithelium  superiorly;  and,  dipping  down 
into  the  longitudinal  folds,  that  inferior  layer  forms  the  chorioid 
plexuses  of  the  third  ventricle,  which  are  continuous  with  those 
of  the  lateral  ventricles  through  the  interventricular  foramina. 
At  the  back  part  in  the  middle  line,  there  is  a  pouch-like  evagina- 
tion  of  the  roof  of  the  diencephalon  in  the  embryo,  which  develops 
into  the  pineal  body;  and  there  remains  a  slight  pit,  called  the 
pineal  recess,  in  the  adult  condition.  A  second  evagination  occurs 
just  above  the  pineal  recess,  which  forms  the  epipineal  recess. 
Pineal  Body.      {Corpus  pineale.  Figs.  40,  43  and  76). — It  is  a 


THE    THIRD    VENTRICLE    AND    INTER-BRAIN. 


133 


THE    THIRD    VENTRICLE    AND    INTER-BRAIN.  1 35 

cone-shaped  body,  a  ciuarlcr  of  an  inch  high  and  one-sixth  of  an 
inch  in  diameter,  joined  to  the  roof  of  the  third  ventricle  by  a 
flattened  stalk  or  peduncle.  It  is  also  called  the  epiphysis.  The 
pineal  body  is  situated  in  the  floor  of  the  transverse  fissure  of 
the  cerebrum,  directly  below  the  splenium  of  the  corpus  callosum 
and  rests  between  the  superior  colHculi  of  the  quadrigeminal 
bodies  on  the  posterior  surface  of  the  mid-brain.  It  is  closely 
invested  by  pia  mater.  The  pineal  stalk  splits  into  a  dorsal  and 
a  ventral  lamina,  which  are  separated  by  the  pineal  recess.  The 
ventral  lamina  fuses  with  the  posterior  commissure;  but  the 
dorsal  stretches  forward  over  the  commissure  in  continuity  with 
the  roof  epithelium.  The  border  of  the  dorsal  lamina  is  thick- 
ened along  the  line  of  attachment  to  the  thalamus  and  forms  the 
stria  medullaris  thalami  {pineal  stria).  The  thickening  is  due 
to  the  presence  of  a  bundle  of  fibers  derived  from  the  columna 
of  the  fornix  and  the  medial  stria  of  the  olfactory  tract.  Between 
the  medullary  striae,  at  the  posterior  end,  there  is  a  transverse 
band,  called  the  habenula.  The  habenula  contains  the  commis- 
sura  habenularum,  through  which  the  fibers  of  the  striae  partially 
decussate  to  the  nucleus  habenulae  in  the  thalamus. 

The  interior  of  the  pineal  body  is  made  up  of  closed  follicles 
surrounded  by  ingrowths  of  connective  tissue.  The  follicles  are 
filled  with  epithelial  cells  mixed  with  calcareous  matter,  the 
brain-sand  (acervulus  cerebri).  Calcareous  deposits  are  found 
also  on  the  pineal  stalk  and  along  the  chorioid  plexuses.  The 
function  of  the  pineal  body  is  unknown.  It  is  supposed  to  repre- 
sent a  cyclopian  eye.  In  the  Hatteria,  a  New  Zealand  Hzard, 
it  projects  through  the  parietal  foramen  and  presents  an  imper- 
fect lens  and  retina  and,  in  its  long  stalk,  nerve  fibers. 

The  chorioid  tela  of  the  third  ventricle  (velum  interpositum, 
Figs.  37,  40  and  42)  is  the  double  triangular  fold  of  pia  mater 
spread  over  the  dorsum  of  the  inter-brain.  It  lies  underneath 
the  fornix  and  the  chorioid  epithelial  lamina  which  stretches 
from  the  body  of  the  fornix  lateralward  to  the  stria  terminalis. 
Its  apex  is  just  behind  the  anterior  commissure,  and  its  base, 
directed  backward,  is  continuous,  by  the  upper  layer,  with  the 
pia  mater  of  the  occipital  lobes;  and,  by  the  inferior  layer,  it  is 


136  THE    CEREBRUM. 

continuous  with  the  pia  on  the  posterior  surface  of  the  mid-brain 
and  cerebellum.  Each  border  constitutes  the  chorioid  plexus 
of  the  lateral  ventricle,  and  is  seen  (through  the  epithelium)  in 
the  floor  of  its  central  part.  The  median  part  of  the  inferior 
lamina  of  the  chorioid  tela  invests  the  roof  epithelium  of  the  third 
ventricle,  and,  the  lateral  portion  covers  the  medial  half  of  the 
upper  surface  of  each  thalamus.  This  layer  forms  the  two  chorioid 
plexuses  of  the  third  ventricle,  which  depend  from  its  median  por- 
tion, Between  the  inferior  and  superior  laminae  is  enclosed  some 
connective  tissue  through  which  the  internal  cerebral  veins  run 
backward  to  the  base  of  the  tela;  there  they  unite  and  form  the 
great  cerebral  vein  (Galeni). 

Anterior  Wall. — ^The  anterior  commissure  {commissura  an- 
terior cerebri.  Figs.  29,  40  and  73)  is  a  very  distinct  round  bundle 
of  white  fibers  about  an  eighth  of  an  inch  in  diameter.  It  is  seen 
in  the  anterior  wall  of  the  third  ventricle  supporting  the  roof 
epithelium.  The  epithelium  there  bends  down  between  the 
columnee  of  the  fornix  and  invests  the  ventricular  surface  of  the 
commissure.  The  columnas  of  the  fornix  and  the  commissure 
bound  the  recessus  triangularis,  in  which  the  roof  and  anterior 
wall  of  the  third  ventricle  meet.  The  anterior  commissure  rests 
upon  the  upper  extremity  of  the  lamina  terminalis,  between  the 
columnae  fomicis,  behind,  and  the  lamina  rostralis  of  the  corpus 
callosum,  in  front.  With  the  last  two  structures  it  is  developed 
in  the  lamina  terminalis.  It  is  the  most  important  connecting 
link  between  the  hemispheres  in  vertebrates  without  a  corpus 
callosum  (all  below  mammals).  Bending  sharply  backward 
in  the  cerebral  hemisphere  the  anterior  commissure  pierces  the 
inferior  part  of  the  globus  pallidus  and  then  radiates  toward  the 
cortex,  some  of  its  fibers  entering  the  external  capsule.  It  con- 
tains two  groups  of  fibers:  (i)  The  anterior  group,  which  is  the 
commissure  of  the  rhinencephalon,  called  the  pars  olfactoria; 
and  (2)  the  posterior  group,  the  pars  occipito-temporalis.  The 
pars  olfactoria  probably  contains  two  fasciculi:  (a)  A  commis- 
sural bundle  which  bends  sharply  downward  to  the  olfactory 
tracts  and  joins  the  two  olfactory  bulbs  together;  and  (b)  a 
decussating  bundle  which  joins  each  olfactory  bulb  to  the  opposite 


THE    THIRD    VENTRICLE    AND    INTER-BRAIN. 


Fig.  40. — Horizontal  section  of  cerebrum  through  genu  and  below  splenium  of 
corpus  callosum.  Fornix  and  chorioid  tela  turned  back,  to  show  inter-brain 
and  third  ventricle.     (Original.) 

a.  Head  of  caudate  nucleus,  b.  Stria  medullaris  thalami  (or  pineal  stria.)  c.  Chorioid 
groove,  d.  Trigonumhabenulae.  _e.  Pineal  body.  f.  Tail  of  caudate  nucleus,  g.  Tapetum. 
h.  Occipito-thalamic  radiation,  i.  Inferior  longitudinal  fasciculus,  j.  Anterior  horn  of 
lateral  ventricle,  k.  Columna  of  fornix.  1.  Recessus  triangularis,  m.  Anterior  commissure, 
n.  Massa  intermedia  (or  middle  commissure),  o.  Posterior  commissure,  p.  Superior  quad- 
rigeminal  colliculus.    q.  Posterior  horn  of  lateral  ventricle. 


THE    THIRD    VENTRICLE    AND    INTER-BRAIN.  1 39 

uncus  and  amygdala.  The  pars  occipito-teniporalis  connects 
the  tentorial  areas  of  the  two  hemispheres  together,  regions  which 
are  not  connected  by  the  corpus  callosum.  In  man  it  is  larger 
than  the  pars  olfactoria.  A  thin  transverse  sheet  of  gray  matter, 
called  the  lamina  terminalis,  extends  downward  and  forward 
from  the  anterior  commissure  to  the  optic  chiasma  and  completes 
the  anterior  wall  of  the  ventricle  (Figs.  17,  28  and  73).  Between 
the  chiasma  and  the  lamina  terminalis  is  a  sharp  angle  which 
terminates  on  either  side  in  a  small  pit,  called  the  optic  recess. 

The  floor  of  the  third  ventricle  is  ver}^  narrow  (Figs.  21  and 
27).  It  is  formed  by  the  interpeduncular  structures  plus  the 
tegmenta,  namely:  optic  chiasma,  tuber  cinereum  and  infundibu- 
lum,  corpora  mammillaria,  posterior  perforated  substance  and 
the  tegmenta.  The  last  two  are  portions  of  the  mid-brain;  the 
others  belong  to  the  fore-brain  with  the  surface  of  which  we  have 
already  studied  them,  and  all  extend  laterally  beneath  the  thalami. 

The  third  ventricle  has  its  lateral  wall  formed  chiefly  by  the 
thalamus  and  the  columna  of  the  fornix  (Figs.  27  and  28).  Below 
a  slight  longitudinal  groove,  extending  from  the  optic  recess 
to  the  cerebral  aqueduct  and  called  the  sulcus  hypothalamicus-, 
the  thalamus  is  covered  by  upturned  hypothalamic  gray  matter 
and.  by  the  upper  part  of  the  central  gray  substance  of  the  mid- 
brain. The  thalamus  forms  the  immediate  lateral  wall  above 
this  hypothalamic  groove.  The  columna  of  the  fornix,  diverging 
from  its  fellow,  proceeds  downward  and  backward  to  the  corpus 
mammillare  through  the  medial  part  of  the  thalamus.  In  the 
ventricle,  the  pars  libera  of  the  columna  fornicis  is  covered  by 
the  ependymal  epithelium.  It  bounds  the  interventricular  fora- 
men in  front. 

Thalamus.  {Thalamus — a  bed,  Figs.  40,  42,  43  and  44).: — It  is 
the  great  ganglion  of  the  inter-brain.  The  thalamus  is  an  impor- 
tant sensory  relay  station.  In  it  or  in  the  hypothalamic  nuclei 
almost  every  impulse  of  general  sensation,  in  its  journey  to  the 
cerebral  cortex,  is  transferred  to  a  higher  neurone.  The  third 
ventricle  separates  the  thalami  from  each  other,  except  at  the 
mid-point  where  they  are  joined  by  the  massa  intermedia.  The 
thalamus  is  situated  behind  and  medial  to  the  corpus  striatum, 


I40  THE    CEREBRUM. 

and  projects  backward  over  the  mid-brain.  Laterally,  it  rests 
against  the  superior  lamina  of  the  internal  capsule,  which  separates 
it  from  the  lentiform  nucleus.  The  thalamus  is  shaped  like  an 
egg,  with  the  small  end  directed  forward.  It  has  an  anterior  and 
a  posterior  extremity  and  four  surfaces:  Superior,  inferior, 
medial  and  lateral. 

Extremities. — ^The  anterior  extremity  of  the  thalamus  is  lost 
in  a  large  group  of  fibers  (frontal  stalk)  which  runs  through  the 
frontal  part  of  the  internal  capsule.  The  posterior  end  (Fig.  44) 
presents  a  large  pillow-like  prominence,  the  pulvinar,  and  beneath 
it,  are  two  smaller  swellings ;  the  outer  one,  which  forms  the  lowest 
point  of  the  thalamus,  is  the  lateral  geniculate  body;  the  medial 
geniculate  body  is  the  other.  The  two  geniculate  bodies  constitute 
the  metathalamus  (Fig.  43). 

Surfaces. — ^The  medial  surface  of  the  thalamus  forms  the 
immediate  lateral  wall  of  the  third  ventricle  as  far  down  as  the 
sulcus  hypothalamicus  (Fig.  28).  It  is  joined  to  the  internal 
surface  of  the  opposite  thalamus  by  the  massa  intermedia.  It  is 
bounded  above  by  the  medullary  stria.  The  superior  surface  is 
composed  of  a  thin  lamina  of  longitudinal  white  fibers,  derived 
from  the  optic  tract  and  radiation,  called  the  stratum  zonale. 
The  superior  surface  of  the  thalamus  is  divided  by  an  oblique 
groove,  the  chorioidal  groove,  corresponding  in  position  to  the 
border  of  the  fornix,  into  two  areas — a  medial  and  lateral  (Fig. 
44).  The  medial  area  is  covered  by  the  chorioid  tela  of  the  third 
ventricle  and  the  fornix.  Internally,  it  is  bounded  by  the  medul- 
lary stria  of  the  thalamus.  Posteriorly,  next  the  stria,  is  a  tri- 
angular depression  bounded,  behind,  by  a  transverse  groove  in 
front  of  the  corpora  quadrigemina,  and  by  a  slight  groove,  the 
sulcus  habenulae,  externally.  That  depressed  surface  is  called 
the  triangle  0}  the  habenula  (trigonum  habenulae).  Beneath  the 
triangle  is  one  of  the  thalamic  nuclei,  the  nucleus  habenula.  The 
lateral  area  of  the  superior  surface  is  seen  in  the  floor  of  the  lateral 
ventricle.  It  presents  an  anterior  elevation,  the  anterior  tubercle 
{tuber culum  anterior  thalami),  beneath  which  is  the  anterior 
nucleus  of  the  thalamus.  The  chorioid  sheet  of  epithelium, 
extending  from  the  fornix  to  the  stria  terminalis,  covers  this  outer 


THE    THIRD    VENTRICLE    AND    INTER-BRAIN. 


141 


Ant.  Co/^MJssi/i!c 

Op-riC    R  ECS  AS 
f'T    ofInFUNDIBulum 


Fig.  41. — Lateral  and  dorsal  view  of  the  ventricles.  Diagrammatic.   {Original.) 
A.  Lateral  view  of  the  ventricles.    B.  Dorsal  view  of  the  ventricles. 


THE    THIRD    VENTRICLE    AND    INTER-BRAIN.  I43 

area  and  separates  it  from  the  ventricular  cavity.  A  lamina 
of  fibers,  the  external  medullary  lamina,  forms  the  lateral  surface 
of  the  thalamus  and  rests  upon  the  superior  lamina  of  the  internal 
capsule.  Its  fibers  are  continuous  with  those  of  the  capsule.  The 
inferior  surface  blends  with  the  superior  surface  of  the  tegmen- 
tum and  substantia  nigra,  and  forms  the  laminae  and  nuclei  of  the 
tegmental  hypothalamic  region.     (See  below.). 

Tegmental  Hypothalamic  Region  (Figs.  30  and  42). — ^The 
regio  tegmentalis'  hypothalami  is  composed  of  three  layers:  (i) 
Stratum  dorsale  next  the  thalamus;  (2)  zona  incerta,  the  mid- 
dle; and  (3)  hypothalamic  nucleus,  the  inferior.  The  nucleus 
hypothalamicus  (Luysi)  is  ventro-Iateral  in  position  and  lies 
between  the  base  of  the  internal  capsule  and  the  zona  incerta. 
Like  the  substantia  nigra  just  below  it,  it  is  composed  of  pigmented 
gray  matter.  The  reticular  formation  of  the  tegmentum,  con- 
tinuing beneath  the  thalamus,  forms  the  zona  incerta.  The 
stratum  dorsale  is  made  up  as  follows:  (a)  Fibers  from  the 
medial  longitudinal  bundle  (Meynert);  (b)  the  brachium  con- 
junctivum  (Forel),  in  which  is  the  upper  end  of  the  red  nucleus 
of  the  tegmentum;  and  (c)  the  medial  fillet,  which  runs  lateral 
and  slightly  ventral  to  the  red  nucleus. 

The  lateral  geniculate  body  (corpus  geniculatum  laterale,  Fig. 
43)  forms  a  slight  swelling  at  the  low^est  point  of  the  thalamus. 
It  marks  the  apparent  end  of  the  lateral  root  of  the  optic  tract 
and  is  the  terminal  nucleus  of  eighty  per  cent,  of  its  fibers.  It  is 
joined  to  the  superior  quadrigeminal  eminence  by  the  brachium 
superius.  In  appearance  it  is  dark  colored  and  laminated;  its 
gray  matter,  which  contains  pigmented  multipolar  cell-bodies,  is 
divided  into  thick  layers  by  thin  laminae  of  fibers  from  the  optic 
tract  and  radiation.  The  processes  of  the  multipolar  cell-bodies 
help  to  form  the  optic  radiation. 

The  medial  geniculate  body  (corpus  geniculatum  mcdiale), 
also  belongs  to  the  inter-brain  and,  together  with  the  lateral 
geniculate  body,  constitutes  the  metathalamus  (Fig.  43).  It  is 
placed  at  the  end  of  the  medial  root,  as  the  lateral  geniculate  is 
at  the  end  of  the  outer  root,  of  the  optic  tract.  It  rises  up  from 
the   groove    between   the    thalamus    and    corpora   ciuadrigcmina, 


144  THE    CEREBRUM. 

and  is  joined  to  the  inferior  quadrigeminal  eminence  by  the 
brachium  inferius.  The  brachium  superius  sweeps  around  it  in 
front.  The  medial  geniculate  body  is  gray  in  color  and  is  not 
laminated.  Its  cell-bodies  are  small,  and  fusiform  in  shape. 
They  perhaps  give  origin  to  the  intercerebral  fibers  (Guddeni) 
of  the  optic  tract  and  to  a  large  part  of  the  acustic  radiation. 

CEREBRUM. 
SECTION  II.     THE  MID-BRAIN. 

(MESENCEPHALON.) 

The  third  division  of  the  cerebrum  is  the  mid-brain  (Figs. 
44  and  45).  It  is  situated  below  and  behind  the  inter-brain  and 
forms  the  connecting  Hnk  between  the  fore-brain  and  the  hind- 
brain.  This  has  suggested  the  name  "isthmus,"  sometimes 
applied  to  it:  though  isthmus  rhomhencephali  refers  only  to  the 
constriction  below  the  corpora  quadrigemina.  The  mid-brain 
is  developed  from  the  middle  of  the  brain  vesicles,  the  mesencepha- 
lon (Figs.  16,  17  and  18).  The  cavity  of  the  mesencephalon 
persists  as  the  cerebral  aqueduct,  which  is  reduced  to  a  slender 
canal  by  the  -thickening  of  its  walls,  roof  and  floor,  due  largely 
to  the  ingrowth  of  fibers  from  other  parts  of  the  brain.  The 
cerebral  hemispheres  almost  conceal  the  mid-brain  from  view; 
they  overhang  it  dorsally,  and  the  temporal  lobes,  inclosing  it 
between  them,  bend  medially  and  cover  part  of  its  anterior  surface. 
Only  the  median  part  of  the  anterior  surface  is  visible  in  the 
complete  brain  (Fig.  21).  The  form  of  the  mid-brain  resembles 
a  flattened  cylinder.  Its  axis,  a  half  inch  long,  is  pointed  upward 
and  forward,  and  its  long  diameter,  which  varies  from  an  inch 
to  an  inch  and  a  half  in  length,  is  directed  transversely. 

SURFACES. 

The  mid-brain  has  four  surfaces,  viz.,  the  anterior  and  posterior, 
which  are  free,  and  the  superior  and  inferior,  representing  the 
ends  of  the  cylinder,  which  are  attached.  The  two  latter  are 
parallel  with  each  other  and  are  formed  by  section. 

The  superior  surface,  sloping  downward  and  forward,  meets 


SURFACES. 


145 


the  anterior  surface  at  an  acute  angle.  Its  inclination  is  that  of 
the  posterior  end  of  the  floor  of  the  third  ventricle.  External  to 
the  fltoor  of  the  ventricle,  it  is  attached  to  the  thalami  and  internal 
capsules.  The  blending  of  it  with  the  thalami  forms  the  structures 
of  the  tegmental  hypothalamic  regions,  and  the  continuations 
of  the  extreme  lateral  portions,  the  bases  pedunculi,  enter  into 
the  internal  capsules  of  the  hemispheres.     In  the  median  hne 


a'^^        ,.i;5iS''^!''"'^'M\'^'7''i'''''V5''"''^ 


Fig.  42. — Transverse  section  of  brain,  cutting  corpora  mammillaria. 
(After  Toldt,  Morris's  Anatomy.) 

a.  Lateral  ventricle  (central  portion),  b.  Chorioid  plexus  of  lateral  ventricle,  c.  Caudate 
nucleus,  d.  Massa  intermedia,  e.  Internal  capsule.  Lenticular  nucleus:  f,  Putamen; 
gh.  Zones,  globus  pallidus.  i.  External  capsule,  j.  Claustrum.  k.  Ansa  penduncularis.  1.  Optic 
tract,  m.  Inferior  peduncle  of  thalamus,  n.  Inferior  cornu  of  lateral  ventricle,  o.  Hippo- 
campus, p.  Digitations.  q.  Oculomotor  ner^'e.  r.  Corpus  callosum.  s.  Fornix,  t.  Third 
ventricle,  u.  Thalamus,  v.  Thalamo-mammillary  fasciculus,  w.  Ansa  lenticularis.  x.  Hy- 
pothalamic nucleus  (corpus  Luysi).  y.  Substantia  nigra,  z.  Basis  of  cerebral  peduncle. 
aa.  Corpus  mammillare.    bb.  Interpeduncular  fossa,     cc.  Pons  (varolii.) 

behind  the  third  ventricle  it  is  attached  to  the  posterior  commis- 
sure.    The  superior  surface  is  an  inch  and  a  half  broad. 

The  inferior  surface  joins  the  upper  surface  of  the  pons.  It 
is  a  little  narrower  than  the  superior  surface.  It  is  about  one 
inch  and  a  quarter  broad  and  measures  an  inch  dorso-ventrally. 

The  anterior  surface  (ventral)  of  the  mid-brain  looks  forward 
and  downward  (Figs.  45,  47  and  48).     It  is  deeply  grooved  longit- 


146  THE    CEREBRUM. 

udinally  by  a  median  sulcus,  the  fossa  inter  peduncular  is,  and  is 
slightly  concave  from  above  downward.  It  is  separated  on  either 
side  from  the  posterior  surface  by  the  sulcus  lateralis  mesencephali. 
Though  partially  concealed  by  the  temporal  lobes  of  the  cerebrum, 
the  anterior  surface  is  unattached.  It  is  formed  by  a  prominent 
band,  the  basis  pedunculi  at  either  side ;  and  by  a  median  structure, 
the  posterior  perforated  substance  which  is  inclosed  between  the 
two  bases.  The  posterior  perforated  substance  forms  the  floor 
of  the  median  sulcus.  The  inner  border  of  the  basis  pedunculi 
is  free  and  overhangs  the  perforated  substance  slightly.  Thus 
is  formed  the  oculomotor  groove  (sulcus  nervi  oculomotorii)  between 
the  basis  and  perforated  substance  whence  the  third  cerebral 
nerve  takes  its  apparent  origin.  The  fourth  nerve  courses  forward 
over  the  anterior  surface,  but  is  not  attached  to  it. 

The  posterior  surface  (dorsal)  of  the  mid-brain  (Fig.  44), 
though  free,  is  entirely  concealed  by  the  cerebellar  and  cerebral 
hemispheres.  It  forms  part  of  the  floor  of  the  transverse  fissure 
of  the  cerebrum  and  is  covered  by  pia  mater.  The  lateral  sulcus 
bounds  it  on  each  side.  From  the  sulcus  lateralis  it  elevates 
abruptly  toward  the  median  line,  where  it  presents  a  longitudinal 
groove.  This  produces  two  ridges  which  are  subdivided  by 
a  transverse  groove  into  the  four  eminences,  the  colliculi  of  the 
corpora  quadrigemina.  On  either  side,  anterior  and  a  little 
external  to  the  quadrigeminal  bodies,  is  the  medial  geniculate 
body,  joined  to  the  inferior  quadrigeminal  colliculus  by  an  oblique 
ridge,  called  the  brachium  i?iferius.  The  nearly  parallel  longit- 
udinal ridges  below  the  corpora  quadrigemina  are  formed  by 
the  brachia  conjunctiva  of  the  cerebellum.  The  bottom  of  the 
groove  between  them  is  formed  by  the  superior  medullary  velum 
(of  Vieussens),  whence  the  trochlear  nerve  (fourth)  is  seen  issuing. 

r     I.  Corpora  quadrigemina  and  Brachia. 

lU'rl  V,     •     -'  f  ^'  Tegmenta 

1    II.  Pedunculi  \  2.  Substantia  nigra 
[  [3.  Bases  pedunculi. 

The  four  colliculi  of  the  corpora  quadrigemina  and  the  four 
brachia  connecting  them  with  the  geniculate  bodies   constitute 


SURFACES. 


147 


the  quadrigeminal  lamina,  which  forms  the  greater  part  of  the 
posterior  surface  of  the  mid-brain  (Fig.  44).  This  lamina  rests 
upon  the  dorsum  of  the  pedunculi  cerebri.  The  peduncuH  cerebri 
are  made  up  of  three  great  divisions,  as  shown  above;  named  from 
before  backward,  they  are:  (i)  The  bases  pedunculi,  comprising 
the  anterior  part;  (2)  the  substantia  nigra,  which  is  the  middle 
part;  and  (3)  the  tegmenta,  which  are  united  by  a  median  raphe 

h    i 


Fig.  43. — The  region  of  the  mid-brain  showing  pulvinar  of  the  thalamus,  the  gen- 
iculate bodies,  the  corpora  quadrigemina  and  brachia,  the  pineal  body,  the 
optic  tract  and  the  fourth  nerve.     (Original.) 

""a.  Chorioid  groove,  b.  Medial  geniculate  body.  c.  Lateral  geniculate  body.  d.  Medial 
and  lateral  roots  of  optic  tract,  e.  Optic  tract,  f .  Optic  chiasma.  g.  Brachium  inferius. 
h.  Superior  colliculus  of  corpora  quad.  i.  Pineal  body.  j.  Inferior  colliculus  of  corpora 
quad.  k.  Brach.  superius.  1.  Thalamus,  m.  Fraenulumveli.  n.  Superior  medullary  velum. 
o.  Fourth  ventricle,     p.  Trochlear  nerve. 

and  he  in  the  posterior  region  next  the  quadrigeminal  lamina. 
In  the  median  plane  betw^een  the  quadrigeminal  lamina  and  the 
tegmenta  runs  the  cerebral  aqueduct. 

The  bases  pedunculi  (Figs.  45,  46,  47  and  48)  are  two  rounded 
bands  of  medullated  libers,  hmited  by  the  interpeduncular  fossa 
and  lateral  sulcus  of  the  mid-brain.  Each  basis  pedunculi  is  a 
half-inch    broad    and    is    distinctly    striated     longitudinally.     It 


148  '         THE    CEREBRUM. 

issues  from  the  under  surface  of  the  fore-brain  at  the  junction  of 
the  hemisphere  with  the  thalamus  and,  trending  toward  the 
median  Hne,  descends  to  the  pons.  At  its  superior  end  it  is  con- 
tinuous with  the  motor  tracts  of  the  internal  capsule.  Four  motor 
tracts  make  up  the  basis  pedunculi,  viz.,  the  intermediate,  the 
temporo-pontal,    the   pyramidal,    and   the  fronto-pontal. 

The  deep  portion  of  each  basis  pedunculi  (Fig.  47)  is  occupied 
by  the  intermediate  bundle,  whose  fibers  rise  in  the  corpus  striatum 
and  terminate  in  the  nucleus  pontis  (Flechsig).  The  superficial 
portion  should  be  studied  in  three  parts. 

(i)  The  outer  fifth  of  each  basis  contains  the  temporo-pontal 
tract  {tractus  cerehro-cortico-pontalis  temporalis).  It  is  composed 
of  efferent  fibers  which  rise  in  the  temporal  cortex,  in  the  superior, 
middle  and  inferior  gyri  (Dejerine);  and,  perhaps,  in  portions 
of  the  occipital  lobe  (Zacher)  and  the  parietal  lobe  (Sioli).  Pro- 
ceeding through  the  inferior  lamina  and  the  occipital  part  of  the 
superior  lamina  of  the  internal  capsule,  and  through  the  lateral 
part  of  the  basis  pedunculi,  they  terminate  chiefly  in  the  nucleus 
of  the  pons;  a  few  end  in  the  motor  nuclei  of  cerebral  nerves 
(Spitzka).  The  fibers  are  probably  interrupted  and  relayed 
in  the  thalarhus  or  lentiform  nucleus.  They  form  a  segment  of 
the  indirect  motor  path.  These  fibers  are  medullated  later  than 
the  pyramidal  tract   (Flechsig). 

(2)  The  middle  three- fifths  of  the  basis  pedunculi  (Figs.  47 
and  48)  is  occupied  by  the  pyramidal  tract  (fasciculus  longitu- 
dinalis  pyramidaUs).  Its  fibers  rise  in  the  anterior  central  gyrus 
of  the  cerebral  cortex;  they  run  through  the  genu  and  anterior 
two-thirds  of  the  occipital  part  of  the  internal  capsule,  form  the 
middle  three-fifths  of  the  basis,  a  part  of  the  anterior  longitudinal 
fibers  of  the  pons,  and  the  pyramid  of  the  medulla.  Below  the 
medulla  they  are  continued  in  the  anterior  and  lateral  pyramidal 
tracts  of  the  spinal  cord.  Those  fibers  of  the  pyramidal  tract 
which  innervate  the  muscles  of  speech  and  of  the  face  run  through 
the  genu  of  the  internal  capsule  and  constitute  the  medial  portion 
of  the  tract  in  the  mid-brain  and  the  accessory  lemniscus  (of 
Bechterew).  Immediately  behind  the  face  fibers,  in  the  capsula 
interna,  and  external  to  them,  in  the  basis  pedunculi,  are  fibers 


SURFACES. 


149 


Fig.  44. — The  dorsal  or  posterior  aspect  of  the  inter-brain,  the  mid-brain,  the 
pons  and  the  medulla.     {Original.) 

a.  Anterior  tubercle  of  thalamus,  b.  Pulvinar  of  thalamus,  c.  Brachium  inferius.  d. 
Inferior  colliculus  of  corpora  quad.  e.  Brachium  conjunctivum.  f.  Corpus  restiforme.  g. 
Brachium  pontis.  h.  Tuberculum  acusticum.  i.  Calamus  scriptorius.  j.  Area  acustica. 
k.  Posterior  median  fissure.  1.  Stalk  of  pineal  body.  m.  Colliculus  superior  of  corpora 
quad.  n.  Medial  geniculate  body.  o.  Superior  medullary  velum,  p.  Median  groove,  q. 
Colliculus  facialis,  r.  Fovea  superior,  s.  Medullary  strise.  t.  Trigonum  n.  hypoglossi.  u. 
Fovea  inferior,     v.  Ala  cinerea.     w.  Taenia  ventriculi  quarti.     x.  Posterior  lateral  sulcus. 


SURFACES.  151 

which  innervate  the  muscles  0}  the  arm.  Still  behind  these,  in 
the  internal  capsule,  and  external  to  them,  in  the  pyramidal 
tract  of  the  basis  pedunculi,  are  fibers  for  tlie  innervation  of  the 
trunk  and  leg  muscles. 

(3)  The  inner  fifth  of  the  basis  pedunculi  is  composed  of  the 
fronto-pontal  tract  (Iractus  cerebro-cortico-pontalis  frontalis) 
(Figs.  47  and  48).  The  origin  of  the  latter  is  probably  in  the 
prefrontal  cortex.  It  is  motor.  This  motor  tract  is  contained 
in  the  frontal  part  of  the  upper  lamina  of  the  internal  capsule. 
According  to  Hoche,  it  is  interrupted  and  relayed  either  in  the 
thalamus  or  striated  body  (Barker).  Its  termination  is  in  the 
nucleus  of  the  pons  and  in  the  motor  nuclei  of  cerebral  nerves 
(Flechsig).  It  constitutes  a  stage  of  an  indirect  motor  path,  like 
the  fibers  of  the  outer  fifth  of  the  basis  peduncuh,  and  the  indirect 
path  is  continued  to  the  opposite  half  of  the  cerebellum  by  neurones 
whose  cell-bodies  are  in  the  nucleus  pontis  (Flechsig). 

The  Substantia  Nigra  (Figs.  46,  47  and  48). — ^The  central  part 
of  the  crura  cerebri  is  a  sheet  of  pigmented  gray  matter.  The 
substantia  nigra  is  visible  at  the  base  of  the  brain  between  the 
bases  pedunculi,  where  it  is  called  the  posterior  perforated  sub- 
stance (substantia  perforata  posterior),  and  its  margin  comes  to 
the  surface  in  each  lateral  sulcus  of  the  mid-brain.  It  extends 
from  the  pons  upward  to  the  corpora  mammillaria  and  nucleus 
hypothalamicus  (Luysi).  Dorsal  to  it  are  the  tegmenta.  Trans- 
versely, the  substantia  nigra  is  convex  forward,  but  it  is  slightly 
concave  longitudinally.  The  third  nerve  pieces  it  and  comes 
out  through  the  oculomotor  groove.  It  contains  small  pigmented 
multipolar  cell-bodies,  some  of  which  constitute  a  relay  for  cer- 
tain fibers  of  the  medial  fillet  (Barker).  There  is  a  median 
aggregation  of  these  cells  located  just  in  front  of  the  pons,  the 
interpeduncular  ganglion  (ganglion  inter  peduncular  e).  According 
to  Forel,  this  ganghon  is  connected  by  a  bundle  of  fibers,  the  fas- 
ciculus retroflexus,  with  the  nucleus  habenulae  of  the  thalamus. 
The  superior  portion  of  the  substantia  nigra  Ues  ventral  to  the 
nucleus  hypothalamicus  (Luysi)  on  cither  side.  The  nucleus 
hypothalamicus  lies  ventro-lateral  to  the  red  nucleus,  and  is 
separated  from  it  by  the  zona  incerta. 


152  THE    CEREBRUM. 

The  Tegmenta  (Figs.  46,  47  and  48). — ^The  posterior  divisions 
of  the  pedunculi  cerebri,  which  cover  the  other  divisions,  are  in 
consequence  called  the  tegmenta  (tegmentum — a  cover).  They 
are  united  by  a  median  raphe  and  fit  ventrally  into  the  concavity 
of  the  substantia  nigra.  They  are  bounded  by  the  lateral  sulcus 
of  the  mid-brain  on  the  free  side,  v^here  each  tegmentum  presents 
a  triangle,  bounded  by  the  sulcus  lateralis,  in  front;  by  the  bra- 
chium  inferius,  above;  and,  inferiorly,  by  the  lateral  fillet.  Dor- 
sally,  the  tegmenta  fuse  with  the  quadrigeminal  lamina  except 
along  the  m^edian  line,  where  the  cerebral  aqueduct  separates  them. 
Each  tegmentum  at  the  superior  end  blends  with  the  thalamus, 
and  helps  to  form  the  tegmental  hypothalamic  structures.  Im- 
bedded in  that  superior  portion  is  the  red  nucleus  (n.  ruber)  of 
the  tegmentum.  (See  tegmental  hypothalamic  region.)  Inferiorly, 
the  tegmenta  are  continued  into  the  reticular  formation  of  the 
pons. 

The  Cerebral  Aqueduct  (Aqueductus  Cerebri,  Sylvii,  Figs.  17,  27 
and  47). — ^The  aqueduct  is  a  very  slender  canal  connecting  the 
third  and  fourth  ventricles.  So  it  is  the  "iter  a  tertia  ad  quar- 
tum  ventriculum."  It  is  situated  in  the  median  line  under  the 
quadrigeminal  lamina  and  produces  a  slight  beveling  of  the  dorso- 
medial  borders  of  the  tegmenta.  It  is  a  half-inch  long.  In  shape 
it  is  v-like,  above;  elliptical,  in  the  middle,  with  a  vertical  major 
axis;  and  T-form,  below,  where  it  joins  the  fourth  ventricle. 
Its  height  varies  between  a  sixteenth  and  an  eighth  of  an  inch. 
Like  other  ventricles,  it  is  lined  with  ependyma.  A  layer  of  gray 
matter,  thickest  on  the  sides  and  floor,  surrounds  the  aqueduct 
of  the  cerebrum.  This  is  the  stratum  griseum  centrale,  which 
gives  rise  to  some  of  the  fibers  of  the  posterior  commissure.  The 
stratum  griseum  centrale  is  continuous  with  the  gray  matter  of 
the  fourth  ventricle.  In  the  ventral  part  of  it  are  the  nuclei  of 
the  oculomotor  (third),  the  trochlear  (fourth)  and  the  trigeminal 
(fifth)  cerebral  nerves. 

Nuclei  0}  the  Oculomotor  and  Trochlear  Nerves  (Figs.  47  and 
48). — ^Both  nuclei  together  extend  the  entire  length  of  the  aque- 
duct, and  the  oculomotor  is  prolonged  into  the  wall  of  the  third 
ventricle,  where  it  receives  a  bundle  of  fibers  from  the  opposite 


SURFACES. 


153 


Fig.  45. — Anterior  aspect  of  the  mid-brain,  pons  and  medulla.     {Original). 

a.  Interpeduncular  fossa,  b.  Basis  pedunculi.  c.  Pons.  d.  Trigeminal  nerve,  e.  Ab- 
ducent nerve,  f.  Acustic  nerve,  g.  Facial  nerve,  h.  (Intermediate  nerve,  i.  Glosso- 
pharyngeal nerve,  j.  Vagus  nerve,  k.  Accessory  nerve.  1.  Hypoglossal  ners'e.  m.  An- 
terior median  fissure,  n.  Optic  tract,  o.  Optic  chiasma.  p.  Optic  nerve,  q.  Stalk  of  in- 
fundibulum.  r.  Corpus  mammillare.  s.  Oculomotor  nerve,  t.  Medial  and  lateral  roots  of 
optic  tract,  u.  Sulcus  basilaris.  v.  Acustic  nerve,  w.  Foramen  caecum  (Vicq  d'Azyri). 
X.  Pyramid,  y.  Olive,  z.  Anterior  lateral  sulcus,  aa.  Posterior  lateral  sulcus,  bb.  Funic- 
ulus lateralis. 


SURFACES.  155 

optic  radialion  and  oplic  tract.  The  nucleus  of  the  third  nerve 
(n.  oculomolorius),  according  to  Perlia,  is  composed  of  seven  dis- 
tinct ccll-groui)s,  scattered  from  the  posterior  part  of  the  lateral 
wall  of  the  third  ventricle  down  to  the  level  of  the  transverse 
groove  between  the  superior  and  inferior  quadrigeminal  collic- 
uli.  From  these  seven  cell-groups  the  axones  proceed  forward 
into  the  nerve  of  the  same  side;  but  there  is,  in  addition,  one 
median  group  of  cell-bodies  which  sends  axones  into  both  nerves. 
The  nuclei  are  also  associated  by  decussating  dendrites.  The 
root  fibers  run  forward  through  the  red  nucleus  and  substantia 
nigra  and  issue  from  the  oculomotor  groove.  The  nucleus  of  the 
fourth  nerve  {n.  trochlearis)  is  a  single  oval  mass  of  cell-bodies 
situated  ventral  to  the  inferior  colhculus  of  the  corpora  cjuadri- 
gemina.  The  root  fibers  of  the  fourth  nerve,  trochlear,  proceed 
dorsally  and  caudalward  from  the  nucleus.  They  decussate 
with  the  fibers  from  the  opposite  nucleus  in  the  superior  medullary 
velum,  from  which  they  emerge  on  either  side  of  the  frenulum. 
They  then  continue  in  the  opposite  nerve  around  the  side  and 
over  the  anterior  surface  of  the  mid-brain.  This  is  the  only  nerve 
that  decussates  en  masse  between  the  genetic  nucleus  and  the 
apparent  origin. 

The  nucleus  0}  the  mesencephalic  root  oj  the  trigeminal  nerve 
is  composed  of  large  cell-bodies  scattered  in  the  extreme  ventro- 
lateral part  of  the  stratum  griseum  centrale,  from  the  highest 
level  of  the  mid-brain  down  to  the  pons.  There  is  no  break  be- 
tween this  nucleus  and  the  chief  motor  nucleus  of  the  fifth  nerve 
formed  by  the  substantia  ferruginea  under  the  locus  casruleus. 
The  axones  of  these  large  cell-bodies  run  do\\Tiward  through 
the  nucleus,  accumulating  gradually  until  they  form  a  distinct 
crescentic  strand,  which  joins  the  chief  motor  root  of  the  same 
side. 

The  opposite  pyramidal  tracts  and,  probably,  the  three  homo- 
lateral cerebro-pontal  tracts  (fronto-pontal,  temporo-pontal  and 
intermediate  tracts)  bring  these  nuclei  into  relation  with  the 
cerebral  cortex;  and  the  anterior  and  the  mc(Hal  longitudinal 
bundles  establish  their  reflex  relation. 

Formatio  Reticularis   (Fig.  47). — Through  the  greater  por- 


156  THE    CEREBRUM. 

tion  of  the  tegmenta  there  are  many  oblique  fibers  interwoven 
with  tracts  of  longitudinal  fibers  so  as  to  produce  a  reticulum  or  net. 
Imbedded  in  the  reticular  formation  ventral  to  each  superior 
quadrigeminal  coUiculus  is  a  mass  of  large  cell-bodies  constituting 
the  nucleus  lateralis  superior.  This  is  the  first  of  the  reticular 
nuclei  and  the  only  one  in  the  mid-brain.  Many  of  the  oblique 
fibers  of  the  formatio  reticularis  pass  through  the  median  raphe 
into  the  opposite  tegmentum;  they  produce  the  tegmental  decus- 
sations, which  are  situated  at  three  successive  levels,  viz.,  the 
superior  colliculus,  the  inferior  colliculus  and  the  isthmus  rhomb- 
encephali. 

The  tegmental  decussations  at  the  level  of  the  superior  quad- 
rigeminal colliculus  (the  fountain  decussations)  are:  (i)  The  dor- 
sal tegmental  decussation  (Meynerti)  through  which  the  ante- 
rior longitudinal  bundle  crosses.  It  is  situated  between  the  red 
nuclei  but  dorsal  to  them.  (2)  The  middle — the  decussation 
of  the  fasciculus  pedunculo-mammillaris.  (3)  The  ventral  teg- 
mental decussation  (ForeH)  in  which  the  tract  from  the  red 
nucleus,  the  rubro-spinal  tract,  crosses  to  the  opposite  side  (Fig. 

47)- 

At  the  level  of  the  inferior  colliculus  (Fig.  48)  is  the  decussa- 
tion of  the  brachium  conjunctivum  (decussatio  brachii  conjunc- 
tivi).     It  crosses  with  its  mate  to  reach  the  opposite  red  nucleus. 

At  the  level  of  the  isthmus  is  located  the  vestibular  com- 
missure, composed  of  fibers  which  connect  the  vestibular  nuclei 
of  the  auditory  nerve.  Intermingled  with  the  above  bundles  of 
crossing  fibers  there  are  many  other  fibers  of  the  formatio  retic- 
ularis. 

Tracts  of  Fibers  in  the  Tegmentum  (Figs.  46,  47  and  48). — 
In  the  reticulum  of  the  tegmentum  there  are  eight  distinct  bundles 
of  longitudinal  fibers,  viz.,  the  anterior  and  the  medial  longit- 
udinal bundles,  the  fillet,  the  spino-thalamic  tract,  the  brachium 
conjunctivum  (superior  cerebellar  peduncle),  the  rubro-spinal  tract, 
the  ohvary  bundle,  and  the  descending  root  of  the  trigeminal 
nerve. 

The  medial  (or  posterior)  longitudinal  bundle  {fasciculus 
longitudinalis  medialis,   Fig.  47)  is  a  compact  strand  of  fibers 


SURFACES. 


157 


running  along  the  median  raphe  just  ventral  to  the  central  gray 
substance.  In  Weigert-Pal  sections  it  shows  clearly  as  a  dark 
triangle  nearly  one-sixteenth  of  an  inch  on  a  side.  The  tract 
will  be  found  in  the  same  relative  position  in  the  ])ons  and  medulla 
oblongata.  In  addition  to  several  very  small  strands  of  fibers 
which  will  be  explained  later,  the  medial  longitudinal  bundle  is 


Fig.  46. — Transverse  section  through  the  corpora  mammillaria  and  the  superior 
colliculi  of  the  corpora  quadrigemina.      {Original.) 

a.  Lateral  geniculate  body.  b.  Thalamus,  c.  Medial  geniculate  body.  d.  Brachium 
superius.  e.  Pineal  body.  f.  Stratum  griseum  centrale.  g.  Superior  colliculus  of  corpora 
quad.  h.  Formatio  reticularis,  i.  Substantia  nigra,  j.  Basis  pedunculi.  k.  Medial  and 
lateral  nuclei  of  corpus  mammillare.  1.  Ventral  tegmental  decussation  (Foreli).  si.  Dorsal 
tegmental  decussation  (Meynerti).  n.  Medial  longitudinal  bundle,  o.  Optic  tract,  p.  Red 
nucleus,     q.  Medial  fillet. 

functionally  composed  of  two  tracts:    (i)  An  ascending  bundle; 
and  (2)  a  descending  bundle. 

(i)  The  ascending  part  of  the  medial  longitudinal  bundle  is 
composed  of  fibers  derived  from  the  gray  matter  of  the  spinal 
cord  and  from  the  terminal  nuclei  of  sensory  cerebral  nerves. 
It  is  the  continuation  of  the  long  ascending  fibers  of  the  anterior 
fasciculus  proprius.  Possibly  a  small  portion  of  the  tract  runs 
through  the  posterior  commissure  to  the  thalamus  and  is  common 
sensory  in  function;  but  the  major  part  of  it  decussates  in  several 


158  THE    CEREBRUM. 

successive  strands  which  end  in  the  opposite  motor  nuclei  of  the 
cerebral  nerves.     The  function  of  this  latter  part  is  reflex. 

(2)  The  descending  part  of  the  medial  longitudinal  bundle 
is  composed  chiefly  of  uncrossed  axones  from  the  large  cell- 
bodies  in  the  nuclei  of  the  reticular  formation.  Beginning  at  the 
nucleus  laieralis  superior  in  the  mid-brain,  it  receives  fibers 
from  each  reticular  nucleus  down  to  the  nucleus  lateralis  inferior 
of  the  medulla.  It  receives  the  largest  accession  of  fibers  in  the 
pons,  where  the  nucleus  lateralis  medius  and  the  three  nuclei 
centrales  are  located.  On  this  account  James  S.  Collier  suggests 
that  it  be  called  the  medial  ponto-spinal  tract.  It  has  been  traced 
through  the  anterior  fasciculus  proprius  to  the  lower  part  of  the 
spinal  cord.  Its  size  is  gradually  reduced  by  the  ending  of  a  few 
fibers  in  the  gray  substance  corresponding  to  each  segment  of  the 
cord. 

In  the  mid-brain  the  medial  longitudinal  bundle  also  contains 
fibers  derived — (i)  from  the  oculomotor  nucleus,  which  descend 
to  the  pons,  and  enter  into  facial  nerve  through  which  they  supply 
the  muscles  of  expression  above  the  eye;  and  (2)  from  the  nucleus 
of  the  abducent  nerve.  Running  upward  and  decussating,  the 
latter  strand  of  fibers  terminates  in  the  opposite  nucleus  of  the 
oculomotor  nerve,  and  thus  innervates  the  internal  rectus  of  that 
eye.  This  strand  accounts  for  the  conjugate  action  of  the  two 
eyes  in  both  health  and  disease. 

The  anterior  longitudinal  bundle  forms  a  distinct  strand 
situated  in  the  formatio  reticularis  ventro-lateral  to  the  medial 
longitudinal  bundle  (Figs.  47  and  48).  It  degenerates  downward 
and  is  a  descending  tract.  It  takes  its  origin  in  the  superior 
colliculus  of  the  corpora  quadrigemina,  whence  it  decussates  at 
once  through  the  dorsal  tegmental  decussation  (Meynerti)  and 
descends  through  the  reticular  formation  of  the  pons  and  medulla; 
and,  then,  through  the  fissural  side  of  the  anterior  column  of  the 
spinal  cord  until  it  fades  away  in  the  lumbar  region.  Only  by 
its  degeneration  has  it  been  located.  Its  fibers  end  in  the  gray 
matter  of  the  cord  on  both  sides  and  in  the  genetic  nuclei  of  cere- 
bral nerves ;  but,  chiefly,  in  the  nuclei  of  the  oculomotor,  trochlear 
and  abducent  nerves  and  in  the  cilio-spinal  center  of  the  spinal 


SURFACES. 


159 


cord.  In  function  the  anterior  longitudinal  bundle  is  reflex; 
it  is  connected  with  all  ocular  reflexes  which  are  excited  by  impulses 
from  the  retinae,  such  as,  accommodation  for  distance,  pupillary 
contraction  and  dilatation. 

The  Fillet  or  Lemniscus  (Figs.  46,  47  and  48). — ^Near  the 
upper  end  of  the  pons,  in  the  ventral  part  of  the  formatio  reticu- 
laris, the  fillet,  or  lemniscus,  forms  a  very  broad  band  of  fibers 


e, 


Fig.  47. — Section  of  the  mid-brain  through  superior  colHcuH  and  the  apparent 
origin  of  the  oculomotor  nerve.     (Original.) 

a.  Sulcus  latemlis  of  mid-brain,  b.  Red  nucleus,  c.  Medial  longitudinal  bundle,  d.  Oculo- 
motor nucleus,  e.  Stratum  griseum  centrale.  f.  Colliculus  superior  of  corpora  quadrigemina. 
g.  Formatio  reticularis,  h.  Medial  fillet,  i.  Medial  geniculate  body.  j.  Optic  tract,  k.  Basis 
pedunculi.  1.  Dorsal  tegmental  decussation  (Meynerti).  m.  Ventral  tegmental  decussation 
(Foreli).  n.  Fossa  interpeduncularis.  o.  Substantia  nigra,  p.  Fronto-pontal  tract,  q.  3d.  N. 
r.  Pyramidal  tract,     s.  Intermediate  tract,     t.  Temporo-pontal  tract. 

on  either  side  of  the  median  raphe.  The  fillet  is  equal  in  width 
to  half  the  transverse  diameter  of  the  mid-brain.  It  continues 
into  the  ventral  portion  of  the  tegmentum,  but  immediately  di^•ides 
into  two  fascicuh,  viz.,  the  medial  fillet,  and  the  lateral  fillet. 
Farther  forward  a  small  bundle  leaves  the  lateral  part  of  the 
medial  fillet  and  runs  up  to  the  superior  quadrigeminal  coUiculus. 
That  bundle  is  called  the  superior  fillet. 


l6o  THE    CEREBRUM. 

Function. — ^The  fillet  forms  a  segment  in  the  direct  sensory 
tract.  It  carries  spinal  and  cerebral  impulses  of  the  tactile  and 
muscular  senses  to  the  corpora  quadrigemina  and  thalamus, 
and  auditory  impulses  to  the  inferior  quadrigeminal  coUiculus. 

T         .  /  L.  Medialis  \  L.  Superior. 

Lemniscus  \   ^    ^    ^      .. 
\  L.  Lateralis 

Medial  Fillet.  {Lemniscus  medialis,  Figs.  47  and  48). — ^The 
fibers  composing  the  medial  fillet  rise  chiefly  in  the  nucleus  funiculi 
gracilis  and  nucleus  funiculi  cuneati  of  the  opposite  side  of  the 
medulla  oblongata.  They  cross  over  in  the  fillet  decussation 
of  the  medulla;  and,  excepting  a  small  bundle,  terminate  in  the 
lateral  nucleus  of  the  thalamus.  Fibers  are  added  from  the 
terminal  nuclei  of  sensory  cerebral  nerves  which  cross  the  median 
plane  and  enter  the  opposite  fillet.  Thus  connected  with  all 
common  sensory  nerves,  and  with  the  vestibular  nerve,  it  enters 
the  mid-brain  and  divides  into  two  parts.  A  small  bundle  of 
fibers  separating  from  the  lateral  part  and  running  to  the  superior 
quadrigeminal  colliculus,  forms  the  superior  fillet.  It  associates 
ocular  movements  with  sensations  from  cerebral  and  spinal  nerves. 
The  medial  fillet  continues  to  the  lateral  nucleus  of  the  thalamus, 
bearing  impressions  of  the  tactile  and  the  muscular  sense.  From 
the  thalamus  the  impulses  are  carried  by  the  cortical  fillet  to  the 
somsesthetic  area  of  the  cortex. 

The  lateral  fillet  (lemniscus  lateralis)  forms  an  oblique 
ridge  on  the  lateral  border  of  the  tegmentum  (Fig.  44).  It  trends 
upward  and  inward  over  the  brachium  conjunctivum  to  the  infe- 
rior quadrigeminal  colliculus  where  some  of  its  fibers  terminate. 
A  few  fibers  continue  to  the  superior  colliculus.  Its  function  is 
auditory  conduction.  It  rises  chiefly  from  the  ventral  and  lateral 
parts  of  the  cochlear  nucleus  (principally  the  opposite  one)  and 
ends  in  the  inferior  quadrigeminal  colliculus.  The  greater 
number  of  its  fibers  cross  through  the  trapezoid  body  and  medul- 
lary striae,  some  are  uncrossed.  It  undergoes  partial  relay  in  the 
nucleus  of  the  superior  olive  and  nucleus  of  the  trapezoid  body  on 
both  sides  and  the  nucleus  of  the  lateral  fillet  on  the  same  side. 

The  lateral  fillet  is  only  partially  relayed  in  the  inferior  col- 


SURFACES. 


l6l 


liculus  of  the  cor])ora  (luadrigcmina,  being  continued  directly 
into  the  brachiiim  inferius.  Auditory  conduction  therefore 
proceeds  from  the  inferior  colHculus  through  the  brachium  inferius 
to  the  medial  geniculate  body  and  then  through  the  acustic  radi- 
ation to  the  temporal  cortex.     Thus  the  lateral  fillet  forms  the 


Fig.  48, 


-Section  of  the  mid-brain  cutting  the  inferior  colliculi  of  the  corpora 
quadrigemina.      (Original.) 


a.  Sulcus  lateralis,  b.  Formatio  reticularis,  c.  Medial  longitudinal  bundle,  d.  Nucleus 
of  colliculus  inferior,  e.  Aqueductus  cerebri,  f.  Rubro-spinal  tract,  g.  Lateral  fillet,  h. 
Medial  filliet.  i.  Basis  pedunculi.  j.  Location  of  anterior  longitudinal  bundle,  k.  Interpedun- 
cular fossa.     L  Substantia  nigra,    m.  Decussation  of  brachia  conjunctiva. 


second  stage  in  the  auditory  conduction  path.  The  acustic 
nerve  constitutes  the  first  stage,  the  lateral  fillet  the  second  stage, 
the  brachium  inferius  the  third,  and  the  acustic  radiation  the 
fourth  stage.  The  last  stage  ends  in  the  cortex  of  the  superior 
and  the  transverse  temporal  gyri. 

The  spino-thalamic  tract  (Figs.  47  and  48)  is  located  in 
the  region  of  the  nucleus  lateralis  superior.  It  is  a  loose  strand 
of  fibers  not  isolated  from  surrounding  structures;  and,  probably, 
has  many  relays  in  its  course.  The  spino-thalamic  tract  rises 
in  the  gray  substance  of  the  spinal  cord  and  in  the  terminal  nuclei 
of  the  common  sensorv  cerebral  nerves.     Thous^h  it  sends  some 


1 62  THE    CEREBRUM. 

fibers  to  the  quadrigeminal  bodies,  the  substantia  nigra  and  tlie 
lentiform  nucleus,  its  chief  termination  is  in  the  lateral  nucleus 
of  the  thalamus.  It  is  sensory.  It  conducts  tactile,  pain  and 
temperature  impressions. 

Brachium  Conjunctivum.  {Superior  cerebellar  peduncle). — 
The  brachium  conjunctivum  form.s  a  ridge  on  the  surface  near 
the  median  line  of  the  isthmus,  which  ends  above  at  the  inferior 
quadrigeminal  coUiculus  (Fig.  44).  The  lateral  fillet  winds 
inward  over  its  upper  extremity.  It  is  joined  to  its  fellow  by  a 
sheet  of  white  matter,  the  superior  medullary  velum.  The  fibers 
of  the  brachia  conjunctiva  bend  ventrally  beneath  the  inferior 
colHculus  of  the  corpora  quadrigemina  and,  for  the  most  part, 
decussate  anterior  to  the  cerebral  aqueduct,  through  the  median 
raphe  (Fig.  48).  These  crossed  fibers  with  the  few  uncrossed 
run  forward  toward  the  inferior  surface  of  the  thalamus,  where 
they  inclose  the  red  nucleus,  and  help  to  form  the  stratum  dorsale 
of  the  hypothalamic  region  (Forel).  Many  of,  the  fibers  terminate 
in  the  red  nucleus  and  from  it  others  rise  and  proceed  forward 
to  the  thalamus.  Though  most  of  the  brachium  conjunctivum 
rises  in  the  cerebellum  and  forms  a  segment  of  an  indirect  sensory 
tract,  it  also  ^contains  eft'erent  fibers  which  rise  in  the  red  nucleus. 

Rubro-spinal  tract  (Crossed  Descending  Tract  of  the  Red 
Nucleus). — Formed  by  axones  of  the  red  nucleus,  it  immediately 
crosses  through  the  ventral  tegmental  decussation  (foreli)  and 
proceeds  lateral  ward  to  the  lateral  fillet  (Fig.  47).  In  the  lower 
part  of  the  mid-brain,  it  is  imbedded  in  the  medial  part  of  that 
fillet.  The  rubro-spinal  tract  runs  through  the  medulla  and 
descends  in  the  spinal  cord  to  the  lumbar  region,  where  it  ends  in 
the  center  of  the  gray  crescent. 

Olivary  Fasciculus. — ^The  olivary  bundle  is  a  loose  strand  of 
fibers  traversing  the  reticular  formation  lateral  to  the  medial 
longitudinal  bundle,  in  the  upper  part  of  the  mid-brain;  in  the 
lower  region  of  the  mid-brain,  it  runs  closer  to  the  median  line 
and  is  mingled  with  the  fibers  of  the  brachium  conjunctivum  as 
they  are  about  to  enter  the  decussation.  The  ohvary  bundle 
probably  rises  in  the  lentiform  nucleus  and  ends  in  the  olivary 
nucleus  of  the  medulla. 


SURFACES.  163 

The  descending  root  of  the  trigeminal  nerve  (Fig.  48) 
rises  in  the  ventro-lateral  part  of  the  central  gray  matter  in  the 
mid-brain  and  is,  therefore,  called  the  mesencephalic  root.  It 
is  a  motor  root.  It  occupies  a  thin  crescentic  area,  just  at  the 
lateral  border  of  the  stratum  griseum  ccntralc,  which  thickens  as 
it  proceeds  downward  toward  the  pons.  This  root  extends  the 
entire  length  of  the  mid-brain ;  but  it  is  made  up  of  very  few  fibers 
in  the  upper  part  and  only  assumes  a  distinct  shape  and  outhne 
when  the  level  of  the  inferior  quadrigeminal  colliculus  is  reached. 
It  is  continued  to  the  middle  of  the  pons  in  the  same  lateral  rela- 
tion to  the  gray  substance;  and  medial  to  the  bracliium  conjunc- 
tivum  cerebelli  it  joins  the  main  part  of  the  motor  root  and  bends 
forward  toward  the  anterior  surface. 

The  Quadrigeminal  Lamina  {Lamina  quadrigemina). — The 
quadrigeminal  lamina  forms  the  fourth  great  division  of  the  mid- 
brain. It  rests  upon  the  dorsum  of  the  tegmenta,  entering  into 
a  large  part  of  the  posterior  surface  of  the  mesencephalon.  A 
crucial  groove  shapes  its  surface  into  four  eminences,  called 
coUiciili  (colliculi  superiores  and  inferiores)  (Fig.  44). 

The  colliculus  superior,  of  either  side,  is  larger  than  the  infe- 
rior colliculus  and  is  circular  in  outline.  It  has  resting  upon  its 
medial  half  the  pineal  body.  It  is  joined  to  the  lateral  geniculate 
body  by  a  band  of  fibers  almost  entirely  concealed  by  the  pulvinar 
of  the  thalamus.  That  band  is  the  brachium  superius.  The 
superior  colliculus  is  made  up  of  gray  substance  for  the  most  part 
(Figs.  46  and  47).  It  is  composed  of  a  superficial  white  layer, 
the  stratum  zonale,  and  a  thick  laminated  gray  layer,  the  stratum 
griseum.  Within  the  stratum  griseum  many  fibers  end;  a  few 
from  the  lateral  fillet,  all  of  the  superior  -fillet,  and  nearly  all  of  the 
hrachium  superius.  The  stratum  griseum  gives  origin  to  the 
anterior  longitudinal  bundle  and,  probably,  to  a  few  fibers  that 
run  through  the  brachium  superius  into  the  optic  ner^•e.  It 
constitutes  an  optic-reflex  center. 

The  colliculus  inferior  of  the  corpora  quadrigemina  is  elong- 
ated transversely  (Fig.  44).  It  is  joined  to  the  medial  geniculate 
body  by  an  oblique  ridge,  called  the  brachium  infer ius,  and  it 
forms  the  termination  of  two  ridges  that  approach  it  from  below, 


164  THE    CEREBRUM. 

due  to  the  lateral  fillet,  and  the  brachium  conjunctivum  of  the  cer- 
ebellum. Its  surface  is  made  up  of  medullated  fibers  continu- 
ous with  the  lateral  fillet  and  brachium  inferius,  which  forms 
the  stratum  zonale ;  gray  substance,  called  the  nucleus  of  the  infe- 
rior colliculus,  constitutes  its  deep  portion.  This  nucleus  receives 
a  part  of  the  lateral  fillet  and  gives  rise  to  a  portion  of  the  brach- 
ium inferius;  it  forms  a  partial  relay  in  the  acustic  path. 

Brachium  Superius  (Figs.  43  and  44). — It  connects  the  lat- 
eral geniculate  body  with  the  superior  quadrigeminal  colliculus; 
but,  excepting  its  extreme  posterior  end,  it  is  buried  in  the  sub- 
stance of  the  thalamus.  Its  course  is  anterior  and  internal  to 
the  medial  geniculate  body.  The  brachium  superius  is  composed 
chiefly  of  efferent  fibers  from  the  optic  radiation,  a  tract  partially 
relayed  in  the  lateral  geniculate  body;  it  probably  contains,  also, 
a  few  optic  fibers  from  the  lateral  root  of  the  optic  tract  and  a 
few  from,  the  stratum  griseum  of  the  superior  quadrigeminal 
colliculus.  Optic  reflex  impulses  are  conducted  by  the  brachium 
superius. 

Brachium  Inferius  (Figs.  43  and  44). — The  inferior  arm, 
connecting  the  inferior  quadrigeminal  colliculus  and  the  medial 
geniculate  body,  is  visible  through  its  whole  length.  It  forms 
the  superior  boundary  of  the  triangle  of  the  lateral  fillet;  the  lateral 
fillet  and  the  sulcus  lateralis  of  the  mid-brain  form  the  other  two 
sides.  Two  sets  of  fibers  make  up  the  brachium  inferius,  viz., 
the  lateral  fillet  fibers  and  the  axones  from  the  nucleus  colliculi 
inferioris.  They  all  terminate  in  the  medial  geniculate  body. 
The  brachium  inferius  forms  the  third  segment  of  the  acustic  path. 

CEREBRUM. 

SECTION  III.    THE  STRUCTURE  OF  THE  CEREBRUM. 
ITS  GRAY  AND  WHITE  MATTER. 

We  have  noticed  in  the  mid-brain  that  the  basis  pedunculi 
and  much  of  the  tegmentum  are  white  matter,  while  the  substantia 
nigra  and  quadrigeminal  colliculi  are  composed  chiefly  of  gray 
substance.  Gray  matter  forms  nearly  all  of  the  inter-brain.  The 
deep  part  of  the  cerebral  hemisphere  is  white  substance,  imbedded 


THE    STRUCTURE    OF    THE    CEREBRUM. 


165 


Fig.  49. — \'arieties  of  neurones  in  the  human  nervous  system. 
(After  Morris's  Anatomy.) 

A.  From  spinal  ganglion.  B.  From  ventral  horn  of  spinal  cord.  C.  Pyramidal  cell  from 
cerebral  cortex.  D.  Purkinje  cell  from  cerebellar  cortex.  E.  Golgi  cell  of  type  II  from  spinal 
cord.  F.  Fusiform  cell  from  cerebral  cortex.  G.  Sympathetic,  o,  axone;  J,  dendrites;  c, 
collateral  branches;  acf,  apical  dendrites;  W,  basal  dendrites;  cc,  central  process;  p.  per- 
pheral  process,  the  dendrite. 


THE    STRUCTURE    OF    THE    CEREBRUM,  167 

in  which  is  the  gray  corpus  striatum.  A  thin  envelope  of  gray 
substance,  called  the  cortex,  forms  the  surface  of  the  hemisj^here. 
The  entire  cerebral  substance,  both  the  white  and  the  gray,  is 
composed  of  neurones  and  suslentacular  tissue,  the  latter  being 
made  up  of  neuroglia,  ependyma  and  mcsoblastic  connective 
tissue.     Of  necessity  the  cerebrum  possesses  a  rich  blood  supply. 

The  Neurone  (Fig.  49). — ^The  essential  element  in  the  nervous 
system  is  the  neurone.  The  neurone  comprises  the  cell-body, 
its  processes  and  end-organs.  The  cell-body,  perikaryon,  or 
neurone  center,  is  a  granular  reticulated  mass  of  protoplasm  of 
variable  form.  It  ranges  in  man  between  four  microns  and  one 
hundred  and  thirty-five  microns  in  diameter.  The  size  of  the 
cell-body  is  usually  proportionate  to  the  length  of  the  processes. 
Its  shape,  which  is  spherical,  fusiform,  pyramidal,  stellate  or  polyg- 
onal, is  dependent  upon  the  number  and  mode  of  origin  of  its 
processes.  The  cell-body  has  a  large  vesicular  nucleus  in  which 
there  are  one  or  more  nucleoli.  It  also  possesses  a  centrosome  in 
spinal  and  sympathetic  ganglia.  Its  reticulated  appearance  is 
due  to  a  net-work  of  fine  fihrillce  which  form  a  close  net  about  the 
nucleus.  These  fibrillse  may  be  seen  in  all  parts  of  the  cell-body 
and  they  are  continued  into  the  processes  given  off  from  it.  ^Masses 
of  deeply  staining  material,  called  tigroid  bodies  or  Nissl  bodies, 
produce  the  granulated  aspect  of  the  perikaryon.  The  tigroid 
bodies  are  found  in  the  receptive  side  of  the  neurone,  viz.,  in  the 
dendrites  and  throughout  the  cell-body,  except  in  the  axone- 
hillock  (Fig.  50). 

The  processes  of  the  neurone  are  from  one  to  eight  or  a  doczn 
in  number  and  are  of  two  kinds,  namely,  the  dendrites  and  the 
axones.  Dendrites,  like  the  cell-body,  are  protoplasmic  in  com- 
position and  of  irregular  contour,  except  in  sensory  nerves,  where 
they  a;re  smooth,  like  axones.  In  all  cases  they  contain  librilloe 
prolonged  from  the  cell-body.  They  branch  riclily  and  end 
in  beaded  points.  The  terminal  branches  are  called  telodendria. 
Dendrites  may  form  synapses  with  axones  of  other  neurones, 
may  terminate  in  special  end-organs,  or  end  free  among  the  cells 
of  any  tissue.  They  are  developed  later  than  the  axones  and 
are  not  always  present.     An  active  cell  usually  has  several  den- 


1 68  THE    CEREBRUM. 

drites.  If  long  they  become  medullated.  Their  conduction  is 
toward  the  cell-body,  cellulipetal,  or  afferent.  Axones,  neurax- 
ones  or  axis-cyhnders  (Fig.  50)  are  smooth  and  fibrillar  in  charac- 
ter. One  (occasionally  two  or  more)  is  given  off  from  the  axone- 
hillock  of  the  cell-body.  It  may  break  up  into  branches  at  once, 
constituting  a  dendraxone;  but  usually  it  runs  a  considerable 
distance  and  sends  out  side  branches,  called  collaterals.  When 
long,  as  a  rule,  it  becomes  medullated  as  its  function  develops,  and 
the  medullary  sheath  presents  segmental  divisions  separated  by 
constrictions,  called  the  nodes  of  Ranvier,  at  which  points  the  col- 
laterals are  given  off.  Both  the  parent  axone  and  all  its  collaterals 
end  by  multiple  division  in  the  form  of  an  end-brush,  or  tassel. 
This  tassel  lies  in  contact  with  the  dendrites  or  body  of  another 
neurone,  with  a  secreting  cell,  or  with  a  muscle  fiber.  In  the  last 
instance  the  fibers  of  the  tassel  spread  out  into  disc-like  plate- 
lets, called  motorial  end- plates  (Fig.  50).  Axone  conduction  is 
from  the  cell-body,  cellulifugal,  or  efferent. 

The  myelin  sheath  of  axones  and  dendrites,  which  is  devel- 
oped as  the  neurone  begins  to  functionate,  is  imbedded  in  neurog- 
lia within  the  optic  nerve  and  tracts,  and  in  the  brain  and  spinal 
cord;  but,  elsewhere,  is  surrounded  by  the  neurolemma  (Schwann) 
and  the  fibrous-sheath  of  Henle.  The  fibers  of  the  olfactory  nerve 
and  most  sympathetic  fibers  are  not  medullated,-  but  they  possess 
the  fibrous  sheath.  Near  the  cell-body  and  near  the  end-tuft 
the  processes  are  naked,  having  neither  the  fibrous  nor  the  medul- 
lary sheath. 

Types  of  Neurones. — i.  The  first  type  has  a  long  axone,  which 
preserves  its  identity,  though  it  may  give  off  many  collaterals. 
Found  in  brain  and  spinal  cord  (Deiters). 

2.  The  second  type  has  a  short  axone,  breaking  at  once  into 
branches  of  apparently  equal  importance,  the  dendraxone.  Found 
in  cerebrurn  and  cerebellum  (Golgi). 

3.  The  third  type  has  two  or  more  axones — diaxone,  triaxone, 
polyaxone — as  in  the  first  layer  of  the  cerebral  cortex  (Cajal). 

Orders  of  Neurones. — i.  The  first  order  has  distal  process 
in  relation  \^dth  the  periphery,  as  spinal-ganglion  and  anterior 
columna  neurones,  and  conducts  from  the  periphery  or  to  it. 


THE  STRUCTURE  OF  THE  CEREBRUM. 


1 69 


Fig.  50. — Motor  neurone.     (After  Barker.) 

a.h.  Axone-hillock  devoid  of  Nissl  bodies,  and  showing  fibrillation,  ax.  Axi.';  cylinder  or 
axone;  this  process  near  the  cell -body,  becomes  surrounded  by  myelin,  m.,  and  a  cellular 
sheath,  the  neurilemma,  the  latter  not  being  an  integral  part  of  the  neurone,  c.  Cytoplasm 
showing  Nissl  bodies  and  lighter  ground  substance,  d.  Protoplasmic  processes  (dendrites) 
containing  Nissl  bodies,  n.  Nucleus,  n'.  Nucleolus.  n.R.  Node  of  Ranvier.  s.f.  Side 
fibrils,  collaterals,  n.  of  n.  Nucleus  of  neurilemma  sheath,  tel.  Motor  end  plate  or  teloden- 
drion.    m.  Striped  muscle  fiber.     s.L.  Segmentation  of  Lantermann. 


THE    STRUCTURE    OF    THE    CEREBRUM. 


171 


2.  The  second  order  has  cell-body  or  distal  process  in  relation 
with  neurone  of  first  order.  It  conducts  to  a  neurone  of  the 
first  order  or  conducts  centrally  from  it.  In  hke  manner  there 
are  neurones  of  the  third,  fourth,  fifth  order,  etc.  ; 

Functions  of  Neurones. — i.  Afferent.  2.  Associative.  3. 
Efferent. 

A  neurone  is  afferent  in  function  when  its  dendrites  are  directed 
toward  the  periphery;  if  its  axone  is  peripherally  directed,   its 


Dendrites 


Nerve-cell 


Axone 
Neurilemma- 


^^ 


Terminal 
branches 


Neurilemma 


..Nerve-cell 


Dendrite 


Fig.  51. — An  efferent  neurone  and  an  afferent  neurone.     (After  Brubaker.) 
A.  Efferent  neurone.      B.  Afferent  neurone. 


function  is  efferent  (Fig.  51).     An  association  neurone  connects 
other  neurones  together. 

Degeneration. — If  a  neurone  is  prevented  from  functionating, 
it  undergoes  a  slow  atrophic  change,  called  degeneration  of  A'^issl. 
Rapid  Wallerian  degeneration  occurs  in  an  axone  or  dendrite  which 
is  completely  cut  off  from  all  other  parts  of  the  neurone.  In  all 
probabihty  neurones  differ  in  chemical  constitution  and  in  electric 


172 


THE    CEREBRUM. 


status,  hence  chemicals,  electricity  and  diseases  appear  to  exer- 
cise a  selective  power  and  afifect  certain  neurones  without  in-" 
fiuencing  others. 

Development  (Figs.  52  and  128). — Every  neurone  is  the  de- 
rivative of  an  epiblastic  cell,  called  the  germinal  cell  of  His,  which 
is  located  in  the  neural  tube  or  crest.  This  germinal  cell,  in 
the  neural  tube,  sends  out  a  process  from  what  was  originally 
its  deep  end,  and  becomes  a  neuroblast.  This  process  forms  the 
axone  and,  later,  dendrites .  are  produced.     During  development 


■  n  O  U   JJ3  ■®i^U  / 

ooqoo 


Fig.  52. — Diagram  showing  development  of  neurones  in  ihe  spinal  cord. 
{McMurrich  after  Schafer.) 

The   circles,  indifferent   cells;  circles  with  dots,  neuroglia  cells;  shaded  cells,  germinal  cells; 
circles  with  cross,  germinal  cells  in  mitosis;  black  cells,  nerve-cells. 


the  cell-body  wanders  more  or  less  from  its  original  position,  and 
thus  reaches  its  adult  location.  The  neurones  are  in  this  manner 
aggregated  into  nuclei  and  cortex.  The  germinal  cells  of  the 
neural  crest  form  bipolar  neuroblasts,  which  send  out  a  process 
from  each  extremity.  The  axone  appears  first,  the  dendrite  later, 
as  in  the  neural  tube.  The  resulting  neurones  make  up  the 
cerebral,  spinal  and  sympathetic  ganglia.  In  the  spinal  ganglia 
and  in  the  common  sensory  cerebral  ganglia,  the  neurones  become 
converted  into  the  unipolar  form  by  the  lateral  growth  of  the  cell- 
body  and  the  fusion,  for  a  short  distance,  of  the  two  processes 


THE  STRUCTURE  OF  THE  CEREBRUM. 


173 


into  one  common  stem  (Figs.  115  and  128).     They  remain  bipolar 
in  the  olfactory  and  acustic  ganglia,  but   form  multipolar  cells 
in  the  sympathetic  gangha. 
Sustentacular  Tissue  (Fig.  53). — In  the  brain  and  spinal  cord 

and  in  the  optic  nerves  two  forms  of  sustentacular  tissue  are 


Fig.  53. — A  section  through  the  spinal  cord  of  a  human  fetus,  23  cm.  in  length. 
Showing  the  central  canal  with  its  substantia  gelatinosa  centralis,  neuroglia 
cells  and  ependyma  cells.     (After  Lenhossek.     Gordinicr's  Nervous  Syskm.) 


found  supporting  the  neurones,,  viz.:  (i)  The  epiblastk  tissue, 
comprising  the  neuroglia  and  the  ependyma:  (A)  Neuroglia 
is  most  abundant  in  gray  matter.  It  is  made  up  of  richly  branched 
nucleated  cells  whose  processes  form  a  fine  reticulation  in  the 


174  THE    CEREBRUM. 

larger  meshes  of  the  connective  tissue  network.  There  are  three 
varieties  of  neurogha  cells,  viz.,  (a)  the  short  rayed  cells,  found 
in  the  cortex  of  cerebellum  and  cerebrum,  the  processes  of  which 
are  strong  and  richly  branched;  (b)  the  long  rayed  cells,  located 
chiefly  in  the  white  substance,  whose  processes  are  long  and  fine 
and  but  little  branched;  and  (c)  the  arborescent  cells,  which  lie 
near  the  surface  in  the  cortex.  Upon  reaching  the  surface  the 
tree-like  branches  form  a  limiting  membrane  of  neuroglia. 

(B)  The  columnar  ciliated  ependymal  cells  which  line  the 
ventricles  are  also  epiblastic  in  origin  and  should  be  classed  with 
the  neuroglia  cells.  They  form  the  only  sustentacular  tissue 
present  in  the  neural  tube  when  it  is  first  formed,  at  which  time 
they  extend  from  the  ventricular  to  the  exterior  surface  of  the 
tube  and,  in  the  peripheral  zone,  form  a  rich  supporting  network. 
They  appear  to  be  of  little  importance  in  the  adult  condition. 

(2)  Connective  Tissue  Network. — ^That  is' of  mesoblastic  origin 
and  is  formed  by  branching  processes  from  the  inner  surface  of 
the  pia  mater.  It  transmits  the  blood-vessels  into  the  nervous 
substance. 

The  neurones  constitute  53  per  cent,  of  the  brain  and  cord 
(cell-bodies,  6  per  cent.)  and  the  sustentacular  tissue  47  per  cent. 
(Donaldson). 

The  white  matter  of  the  cerebro-spinal  axis  is  made  up  chiefly 
of  bundles  of  medullated  axones  imbedded  in  neuroglia  and 
supported  by  connective  tissue.  The  fibers  possess  no  neuri- 
lemma. 

The  gray  matter  of  the,  central  nervous  system  is  composed  of 
cell-bodies  and  dendrites,  chiefly,  but  also  contains  axones.  These 
nerve  elements  are  supported  by  connective  tissue  and  blood-vessels 
and  are  imbedded  in  a  great  abundance  of  neuroglia.  The 
nerve  fibers  in  the  gray  matter  are  to  a  large  extent  non-medul- 
lated  and  naked. 

The  cerebral  gray  substance  {substantia  grisea  cerebri)  is  con- 
veniently divided  into  three  groups  or  classes : 
I.  Cortical. 
II.  Ganglionar. 

III.  Central,  or  ventricular. 


THE    CORTICAL    GRAY    MATTER. 


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THE    ('f)RTI('.\I.    CRAY    MATTF.R.  1 77 

I.     THE  CORTICAL  GRAY  MATTER. 

The  substantia  corticalis  consists  of  a  thin  cn\elopc,  the  cortex 
(or  bark),  which  forms  the  surface  of  the  hemispheres  and  incloses 
the  white  medulla,  the  centrum  semiovalc.  The  cortex  varies  in 
thickness  from  a  line  to  a  quarter  of  an  inch.  Thickest  on  the 
surface  of  the  gyrus,  it  grows  thinner  to  the  bottom  of  the  sulci. 
It  is  of  a  reddish,  or  yellowish-gray  color  dejx'nding  on  llic  richness 
of  the  blood  supply.  By  repeated  observation  of  the  symptoms 
produced  by  definite  brain  lesions  and  by  the  anatomical  and 
physiological  study  of  human  and  lower  animal  brains,  both  in 
the  embryonic  and  adult  condition,  the  cortex  has  been  mapped 
out  into  certain  definite  junctional  areas  (Figs.  54  and  55).  Psychic 
function  undoubtedly  is  dependent  upon  the  associated  activity 
of  a  number  of  cortical  areas;  but  motor,  common  sensory  and 
special  sensory  regions  have  been  outlined  Avith  considerable 
exactness. 

Cortical  or  Cerebral  Localization  (Figs.  54  and  55). — In 
the  following  study  of  the  cerebral  cortex  I  shall  use  very  exten- 
sively the  recent  work  of-  Dr.  Alfred  W.  Campbell,  entitled, 
"Histological  Studies  on  the  Localization  of  Cerebral  Function," 
Cambridge,  England.  In  this  epoch-making  work  we  are  shown 
that  certain  cortical  areas  have  a  characteristic  histological  struc- 
ture that  distinguishes  them  from  all  other  areas.  This  will  be 
referred  to  later  under  "cell  and  fiber  lamination  of  the  cortex," 
but  to  appreciate  this  histological  evidence  of  locahzation  one 
should  thoroughly  study  the  above  work. 

Motor  Area  (Figs.  54,  55,  56  and  57).— The  emissive  motor 
area  is  situated  in  the  anterior  wall  of  the  central  sulcus,  in  the 
posterior  one-half  of  the  gyrus  centralis  anterior  and  in  that  part 
of  the  paracentral  lobule  immediately  continuous  with  it.  This 
is  the  center  for  ordinary  voluntary  motion  on  the  opposite  side 
of  the  body.  Axones  from  this  area  descend  to  the  nuclei  of  all 
motor  nerves.  In  lateral  sclerosis  there  is  degeneration  and 
disappearance  of  the  giant  pyramidal  cells  limited  to  this  motor 
area  (Campbell).  It  is  divided  into  four  segments:  the  head 
and  neck,  the  arm,  the  trunk,  and  the  leg,  named  from  below  up- 
ward.    The  first  extends  to  the  inferior  knee  of  the  sulcus  centralis 


178  THE    CEREBRUM. 

(Rolandi),  though  eye  movements  appear  to  be  represented  in 
the  posterior  end  of  the  middle  frontal  gyrus;  the  arm  area  com- 
prises the  region  between  the  genu  inferius  and  the  genu  superius, 
the  thumb,  fingers,  wrist,  fore-arm,  arm  and  shoulder  move- 
ments being  represented  in  this  ascending  order;  just  above  the 
shoulder  area,  at  the  genu  superius,  is  the  trunk  area;  and  above 
that,  in  the  anterior  central  gyrus  and  in  the  paracentral  lobule, 
in  front  of  the  sulcus  centralis,  is  the  center  for  leg  movements. 
The  representation  in  the  leg  center  is  inverted,  the  ascending 
order  being  hip,  thigh,  leg,  ankle,  toes  and  great  toe. 

The  psychic  motor  areas,  or  areas  for  educated  movements 
are  located  just  anterior  to  the  above  motor  areas,  in  the  anterior 
central  gyrus  and  in  the  contiguous  ends  of  the  superior,  middle 
and  inferior  frontal  gyri  (Figs.  54  and  55).  These  areas  are 
believed  to  send  their  axones  to  the  emissive  motor  centers  in  the 
cortex.  The  psychic  motor  center  for  the  lower  extremity  is 
probably  located  just  in  front  of  its  emissive  motor  center  in  the 
anterior  central  and  superior  frontal  gyri.  In  the  posterior  end 
of  the  middle  frontal  gyrus  is  the  psychic  motor  center  for  the 
arm,  the  writing  center  of  Gordinier;  and  in  the  inferior  frontal 
gyrus  the  center  for  the  organs  of  voice  and  speech,  hence  the 
motor  speech  center.  In  right  handed  people  these  centers  are 
developed  only  in  the  left  cerebral  hemisphere. 

Common  Sensory  Area  (Figs.  54  and  55). — ^According  to  Dr. 
Alfred  W.  Campbell  the  receptive  area  of  common  sensation  is 
limited  to  the  posterior  wall  of  the  sulcus  centralis,  including 
the  anterior  one-half  of  the  posterior  central  gyrus  and  that  part 
of  the  paracentral  lobule  which  is  continuous  with  it.  This  area 
undergoes  exclusive  Nissl  degeneration  in  locomotor  ataxia 
(Campbell).  It  is  probably  divided  into  segments  similar  to 
those  of  the  motor  area  (Spiller). 

Psychic  Sensory  Area  (Figs.  54,  55,  56  and  57). — ^A  large  portion 
of  the  remainder  of  the  parietal  cortex  probably  constitutes  a 
number  of  centers  for  the  interpretation  of  common  sensory 
impulses,  hence  the  term,  psychic  sensory  area.  Impressions 
of  the  muscular  sense  are  believed  to  be  interpreted  in  the  supra- 
marginal  gyrus  and  the  center  of  stereognosis  is  said  to  be  located 


THE  CORTICAL  GRAY  MATTER. 


179 


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THE    CORTICAL    GRAY    MATTER.  l8l 

in  the  superior  parietal  lobule  and  priecuneus.  Perha])S  other 
parts  interpret  tactile,  jjain  and  temperature  impulses.  The 
whole  receptive  and  psychic  area  of  common  sensation  has  been 
called  the  sanuvstJietlc  area  (Barker),  though  the  appUcation  of 
this  term  might  better  be  limited  to  the  receptive  area. 

Acustic  Center  (Figs.  54  and  56). — ^The  receptive  aciistic center 
is  located  in  the  transverse  temporal  gyri  and  in  that  part  of  the 
superior  temporal  gyrus  which  is  continuous  with  them.  In  the 
adjacent  part  of  the  superior  and  middle  temporal  gyri,  in  the 
left  hemisphere,  is  the  psychic  acustic  center. 

Optic  Center  (Figs.  54  and  55). — In  the  cuneus  and  lingual 
gyrus  is  located  the  receptive  optic  center  for  the  temporal  half 
of  the  same  retina  and  the  nasal  half  of  the  opposite  one;  perhaps, 
also,  for  the  macula  lutea  of  both  sides.  The  remainder  of  the 
occipital  lobe  and,  according  to  Mills  and  others,  the  angular 
gyrus,  also,  form  the  psychic  optic  center.  This  latter  center  is 
probably  unilateral  and  developed  only  in  the  left  hemisphere  of 
right  handed  people. 

Olfactory  and  Gustatory  Centers  (Figs.  55  and  57). — The  uncus 
hippocampi  forms  the  chief  cortical  center  of  smell,  close  to  which 
in  the  fusiform  gyrus  is  probably  the  gustatory  center  (Mills). 
Paul  Flechsig  in  his  recent  studies  of  the  human  brain  locates 
taste  in  the  gyrus  cinguli  contiguous  to  the  splenium  of  the  corpus 
callosum  (Fig.  55).  The  olfactory,  auditory,  visual,  common 
sensory  and  motor  areas  are  all  distinguished  by  a  definite  charac- 
teristic histological  structure  peculiar  to  each  region  (Campbell). 
IMedullation  of  the  libers  in  these  cortical  areas  occurs  at  different 
times;  and,  according  to  Flechsig,  in  the  following  order:  olfactory, 
tactile  and  muscular  sense,  visual,  auditory,  and  gustatory. 

In  the  temporal  lobe  ]\Iills  locates  four  other  centers  which 
include  the  pole,  the  inferior  temporal  gyrus  and  a  part  of  the 
middle  temporal  gyrus  (Fig.  56).  These  are  from  before  back- 
ward: the  center  of  intonation  at  the  pole,  the  naming  center,  the 
center  of  equilibration,  and  the  center  of  orientation. 

All  the  above  motor,  somaesthetic  and  special  sense  areas  are 
pro^•ided  with  projection  fibers  which  connect  them  with  defi- 
nite muscle  groups  and  surface  regions  and  with  the  organs  of 


l82 


THE    CEREBRUM. 


special  sense.  Large  parts  of  the  cerebral  cortex  possess  no 
projection  fibers;  they  are  believed  to  be  associative  in  function. 
Association  Centers  of  Flechsig. — ^Flechsig  describes  three  as- 
sociation centers,  the  anterior,  middle,  and  posterior.  Anterior 
Association  Center  (Fig.  54). — ^According  to  Flechsig,  that  part 
of  the  frontal  cortex  which  is  anterior  to  the  motor  region  deter- 
mines the  temperament  and  individuality  of  the  person;  and  as 
Mills  declares,  is  the  center  of  inhibition,  self  control,  attention, 
concentration,  vohtion.     It  is  the  center  of  ''the  abstract  concept'' 


CONCRLTE   CONCEPT 


Fig.  56. — Cortical  areas  after  C.  K.  Mills.     Convex  surface  of  cerebral  hemisphere. 
{Brubaker's  Physiology.) 


(Fig.  56).  J.  S.  Bolton  says  of  this  association  center  that  "it 
is  the  last  part  of  the  cerebrum  to  be  developed,  and  is  the  first 
to  undergo  dissolution;  it  is  under-developed  in  amentia  of  all 
grades  and  atrophied  in  dementia,  according  to  its  degree."  "It 
possesses  the  highest  (mental)  function"  (Brain,  Vol.  29).  The 
posterior  association  center,  composed  of  those  portions  of  cortex 
situated  between  the  sensory  region  of  the  equatorial  zone,  in 
front,  and  the  visual  cortex  of  the  occipital  lobe,  behind,  deter- 


THE    CORTICAL    GRAY    MATTER. 


183 


mines  ihc  intellectuality  of  the  individual  (Fig.  54J.  To  acquire 
knowledge  of  the  external  world  is  thus  the  function  of  the  posterior 
association  center.  Mills  calls  it  the  center  0}  "Ihe  concrete  con- 
cept'' (Fig.  56).  It  includes  three  psychic  areas,  the  common 
sensor}',  auditory  and  visual.  Flechsig  regards  the  island  (of 
Reil)  as  the  middle  association  center  (Figs.  25  and  56).  Lesions 
in  it  are  associated  with  paraphasia. 

Destructive  lesions   of   parts   of   the   motor   or   sensory   cortex 
cause  merely  loss  of  certain  motions  and  sensations  represented 


Fig.  57. — Cortical  areas  after  C.  K.  Mills.     Medial  and  tentorial  surface  of 
cerebral  hemisphere.     {Bnibaker's  Physiology.) 


by  those  parts,  but  ablation  of  association  centers  disconnects 
the  sensory,  the  psychic  and  the  motor  regions  and  causes  aphasia, 
agraphia,  change  of  temperament,  impairment  of  the  so-called 
moral  and  intellectual  faculties,  etc.  Ablation  of  the  visual 
psychic  center  or  auditory  psychic  center  produces  mind-bhndness 
in  the  former  and  in  the  latter  mind-deafness. 

Cell  and  Fiber  Lamination  of  the  Cerebral  Cortex.— There 
is  a  type  of  cerebral  cortex  which,  with  small  but  delinite  varia- 
tions, prevails  throughout  the  cerebrum,  excepting  in  the  visual 


184  THE    CEREBRUM. 

and  olfactory  regions  (Fig.  58).  Though  Dr.  Campbell's  division 
of  the  cortex  into  seven  layers  of  cells  is  complicated,  it  is  similar 
to  Cajal's  description  and  I  think  it  entirely  worthy  of  general 
adoption  and  shall  follow  it  in  this  work.  It  is  to  be  regretted 
that  the  fiber  and  the  cell  layers  have  not  been  more  satisfactorily 
correlated,  as  this  would  assist  in  determining  function.  Dr. 
Arthur  W.  Campbell  gives  the  layers  as  follows: 

First,  the  layers  of  cells : — 

1.  The  plexiform  or  molecular  layer. 

2.  The  layer  of  small  pyramids. 

3.  The  layer  of  medium-sized  pyramids. 

4.  The  external  layer  of  large  pyramids. 

5.  The  layer  of  stellate  or  polymorphous  cells. 

6.  The  internal  layer  of  large  pyramids. 

7.  The  layer  of  fusiform  cells. 

Second,  the  fiber  zones: — 

1.  The  fiberless  layer,  or  neuroglia  zone. 

2.  The  zonal  layer,  stratum  zonale. 

3.  The  supraradiary  zone. 

4.  The  baillargic  zone,  line  of  baillarger. 

5.  The  radiary  zone. 

6.  The  felt-work  of  Kaes. 

I.  The  plexiform  layer  has  next  the  surface  a  fiberless  zone  of 
neuroglia,  on  account  of  which  it  is  often  called  the  neuroglia- 
layer.  Underneath  the  neurogha  is  a  more  or  less  dense  plexus 
of  nerve  fibers,  constituting  the  stratum  zonale;  and  then  an  area 
of  sparsely  scattered  fibers  that  belongs  to  the  supraradiary  zone. 
Scattered  here  and  there  in  the  zonal  and  supraradiary  regions 
of  the  plexiform  layer  are  small  stellate  cell-bodies,  four  or  six 
microns  in  diameter,  belonging  to  the  types  of  Golgi  and  Cajal, 
whose  dendrites  and  whose  double  or  triple  axones  ramify  in  the 
stratum  zonale,  some  near  the  cell-body  and  others  at  a  consider- 
able distance  from  it.  The  stratum  zonale  also  contains  dendritic 
processes  from  subjacent  laminae,  the  T-branched  axones  of 
Martinotti's  cells,  and,  perhaps,  the  end-tufts  of  incoming  fibers 


THE    CORTICAL    GRAY    MATTER. 


Pig  rg  — Cell  and  fiber  lamination  in  the  posterior  half  of  the  anterior  central 
gyrus  The  MOTOR  AREA.  (After  .4.  W.  Campbell's  "Histological  Studies  on  the 
Localization  of  Cerebral  Function."  Published  by  the  Syndics  of  the  Cambndge 
University  Press.) 

A  Stained  to  show  only  fibers.  B.  Stained  to  shmv  only  cell-bodies  z  Stratum  zonale 
S  S^praradian-  zone,  b!  Line  of  Baillarger.  r.  Rad.ary  zone  m  the  deep  part  of  which 
f<;  the  felt -vyork  of  Kaes.  i.  Plexiform  layer.  2.  Layer  of  small  pyramids.  3-  Layer  of 
medium  s' zed  pyramids.  4.  External  layer  of  large  pyramids.  S-  Stellate  or  polymorphous 
cells.     6.  Internal  layer  of  large  pyramids.     7-  Layer  of  fusitorm  cells. 


THE  CORTICAL  GRAY  MATTER.  1 87 

from  the  commissural,  the  associative  and  the  projection  systems. 
It  is  very  well  marked  in  the  motor  area  (Fig.  58),  not  so  well  in 
the  common  sensory  area  (Fig.  59).  In  the  uncus  it  is  very  dis- 
tinct (Fig.  61)  and  is  so  thick  and  dense  in  the  gyrus  hippocampi 
(the  subiculum)  as  to  be  visible  to  the  naked  eye  (Fig.  62).  The 
zonal  layer  of  fibers  is  faint  in  the  visuo-sensory  and  audito- 
sensory  cortex.  The  stratum  zonalc  appears  to  grow  richer 
with  the  education  of  the  individual.  The  function  of  the  plex- 
iform  layer  is  commonly  thought  to  be  association. 

2.  The  layer  of  small  pyramids  (Figs.  58  and  59),  as  well 
as  the  third  layer,  is  situated  in  the  supraradiary  zone.  It  is 
composed  chiefly  of  small  closely  packed  cell-bodies,  pyramidal 
in  shape.  They  measure  eight  or  ten  microns  in  diameter.  Their 
apices  point  toward  the  surface.  From  the  apices,  surfaces  and 
lateral  angles,  dendrites  are  given  off  which  ramify  in  the  stratum 
zonale  of  the  first  layer.  The  axone  issues  from  the  base  of  the 
pyramid  and  runs  down  through  the  subjacent  layers.  Among 
the  small  pyramids  are  a  few  ploymorphous  cells. 

3.  The  layer  of  medium-sized  pyramids  (Fig.  58)  is  a  nearly 
pure  layer;  and,  like  the  overlying  layer,  is  nearly  uniform  through- 
out the  cerebral  cortex.  In  arrangement  of  cell-bodies  and  proc- 
esses it  is  like  the  second  layer.  The  pyramids  get  farther  apart 
and  become  larger  in  size  as  the  layer  is  descended.  They  measure 
ten  to  fifteen  microns  in  their  vertical  diameter.  In  the  anterior 
central  gyrus  these  cells  are  motor.  Layers  "two"  and  "three" 
might  be  combined  in  one  as  was  formerly  the  custom. 

4.  External  Layer  of  Large  Pyramids  (Figs.  58  and  59). — ^This 
layer  coincides  in  position  wth  the  line  of  Baillarger.  The 
Pyramids  are  larger  and  farther  apart  than  in  the  above  layer, 
and  show  a  considerable  accession  of  Nissl  bodies  as  compared 
with  the  smaller  pyramids.  They  measure  15/f  to  2o«  by  25/t 
to  30^,  and  form  "one  of  the  most  important  criteria  in  dividing 
the  brain  surface  into  different  liistological  territories"  (Campbell). 
As  these  cells,  in  the  anterior  central  gyrus,  degenerate  in  amyo- 
trophic lateral  sclerosis,  they  are  considered  motor  in  function. 
The  apical  processes  appear  to  reach  the  first  layer  and  ramify 
in  the  stratum  zonale;  the  lateral  and  basal  dendrites  arborize 


155  THE    CEREBRUM. 

within  the  hne  of  Baillarger;  the  axone  runs  inward  to  the  white 
substance.  The  external  large  pyramids  are  found  in  nearly 
all  parts  of  the  cortex.  They  are  replaced  by  a  layer  of  large 
stellate  cells  in  the  receptive  visual  cortex  along  the  calcarine 
fissure.  The  line  of  Baillarger  in  the  calcarine  cortex  is  so  thick 
and  dense  that  Gennari  and,  later,  Vicq  d'Azyr  described  it  from 
its  naked  eye  appearance  (Fig.  60).  In  the  motor  and  common 
sensory  area  the  line  can  scarcely  be  made  out;  while  in  the  supe- 
rior parietal  gyrus  there  are  two  BaiUargic  lines,  the  deep  line  coin- 
ciding in  .position  with  the  internal  large  pyramids.  There  are 
some  peculiar  Golgi  cells  among  these  pyramids,  whose  axones 
run  horizontally  and  give  off .  collaterals  that  form  pericellular 
baskets  around  the  pyramids  (Johnston).  They  are  associative 
in  function. 

5.  The  layer  of  stellate  or  polymorphous  cells  presents  great 
variation  in  different  regions  and  is  a  valuable  guide  for  cortical 
localization.  It  is  best  marked  in  the  calcarine  area  (Fig.  60) 
where  it  and  the  fourth  .layer  are  associated  with  the  greatly  thick- 
ened BaiUargic  line  {Gennari),  though  elsewhere  it  is  situated 
in  the  radiary  zone  of  fibers.  It  is  well  marked  in  the  auditory 
cortex.  In  the  motor  area  it  is  hardly  distinguishable,  but  it 
appears  suddenly  at  the  bottom  of  the  central  sulcus  and  forms 
a  distinct  feature  in  the  common  sensory  region  of  the  posterior 
central  gyrus  (Fig.  59).  The  cell-bodies  of  the  stellate  layer 
measure  five  to  eight  microns  in  diameter  and  are  of  many  shapes, 
some  being  pyramidal.  They  are  richly  branched.  The  dendrites 
arborize  at  once  near  the  cell-body.  The  axones  of  a  considera- 
ble number  of  cells  extend  horizontally  within  the  layer,  helping 
to  form  the  hne  of  Baiharger;  while  others  run  toward  the  surface 
and  end  in  -the  overlying  laminee. 

6.  Internal  Layer  of  Large  Pyramids  (Fig.  59). — ^This  is  the 
most  important  layer  of  the  cortex  for  localization.  It  hes  in  the 
radiary  zone  of  fibers  and  is  present  in  almost  every  part  of  the 
cerebral  cortex,  though  distinguished  by  definite  variations  in  the 
different  regions  (Figs.  59,  60  and  61).  Its  great  pyramids  are 
intermingled  with  irregular  cell-bodies  of  the  Golgi  type  and 
with  Martinotti  cells.     The  giant  pyramids  (Betz),  or  ganglionic 


THE  CORTICAL  GRAY  MATTER. 


189 


A 


■JL-^ 


Pig.  5g,._Cell  and  fiber  lamination  in  the  anterior  half  of  the  posterior  central 
gyrus.  The  common  sensory  area.  (.'Vfter  A.  W.  CamphelVs  "Histological 
Studies  on  the  Localization  of  Cerebral  Function."  Published  by  the  Syndics  of 
the  Cambridge  University  Press.) 

A.  Stained  to  show  fibers.  B.  Showing  only  cell-bodies,  z.  Stratum  zonale.  s  Supra- 
radiary  zone.  b.  Line  of  Baillarger.  r.  Radiary  zone.  i.  Plexiform  layer.  2.  l^ayer  ot 
small  pyramids.  3.  Layer  of  medium-sized  pyramids.  4-  E.xternal  layer  ot  large  pyramids. 
5.  Layer  of  stellate  cells.     6.  Internal  layer  of  large  pyramids.     7-  Layer  of  fusiform  cells. 


THE    CORTICAL    GRAY    MATTER.  IQI 

cells  (Bevin  Lewis),  arc  "pyraform"  in  shape.  They  are  loaded 
with  Nissl  bodies  and  give  off  one  axone  and  many  dendrites.  The 
lateral  and  basal  dendrites  ramify  in  the  radiary  zone;  the  dendrite 
of  the  summit  runs  straight  out  toward  the  surface  and  Hkc  the 
same  process  from  other  pyramids,  arborizes  in  tlie  stratum  zonale 
of  the  plexiform  layer;  the  axone  enters  the  medullary  substance 
and  becomes  a  projection,  association  or  commissural  fiber. 
The  giant  pyramids  characterize  the  motor  cortex.  No  where 
else  are  they  so  large.  Neither  do  they  have  in  any  other  region 
the  "pyraform"  shape  or  the  definite  nest-like  grouping  seen  in 
the  anterior  central  gyrus.  They  measure  twenty-five  by  sixty 
microns  in  the  leg  area  of  that  gyrus;  twenty  by  forty-five  microns 
in  the  arm  area;  and,  in  the  head  area,  seventeen  by  thirty-five 
microns  (Bevin  Lewis).  In  cases  of  amyotrophic  lateral  sclerosis 
studied  by  Campbell,  87.5  per  cent,  of  these  cells  in  the  affected 
area  were  entirely  destroyed  and  those  remaining  showed  signs 
of  degeneration.  Both  the  internal  and  external  large  pyramids 
were  thus  affected  in  the  anterior  central  gyrus,  so  they  are  motor 
in  that  gyrus;  but  they  were  not  degenerated  in  any  other  part 
of  the  cortex. 

7.  The  fusiform  layer  (Figs.  58,  59,  60  and  61)  is  found 
every  where  in  the  cerebral  cortex.  It  presents  very  little  topo- 
graphical variation.  Its  spindle-shaped  cell-bodies  lie  in  the 
deep  part  of  the  radiary  zone  and  in  the  felt-work  of  Kaes.  The 
long  axes  of  the  spindles  are  perpendicular  to  the  surface  in  the 
crown  of  a  gyrus  but  are  parallel  with  it  in  the  fissural  walls  and 
floor.  From  these  cell-bodies  one  axone  and  several  dendrites 
are  given  off.  The  function  of  the  spindle  cell  is  probably  asso- 
ciation. The  felt-work  of  Kaes  is  a  rich  plexus  of  fibers  in  wliich 
the  white  and  gray  substance  meet.  It  is  produced  by  the  inter- 
mingling of  the  association,  commissural  and  projection  fibers. 
Scattered  here  and  there  through  all  the  layers  of  the  cortex  are 
two  atypical  neurones,  viz.,  the  dendraxones  of  Golgi,  which  arbor- 
ize very  richly  and  are  associative  in  function;  and,  second,  the 
inverted  pyramids  of  Martinotti.  Of  the  latter  the  dendrites 
teiTninate  near  the  cell-body;  but  the  axone  runs  out  to  the  first 
laver    and,    branching   T-like,    ramitics    in    the    stratum    zonale. 


192  THE    CEREBRUM, 

Martinotti's  cells,  like  those  of  Golgi,  are  probably  associative 
in  function. 

The  Radiations  of  Meynert  (Figs.  58,  59,  60  and  61). — ^The  six 
fiber  zones  above  enumerated  have  been  as  fully  indicated  in 
speaking  of  the  cell  lamination  as  the  limits  of  this  work  will 
allow,  but  certain  fibers,  called  the  fibers  of  Meynert,  need  to 
be  mentioned.  The  radiatiojts  of  Meynert  are  strands  of  fibers, 
clearly  visible  in  the  radiary  zone  of  the  cortex,  composed  of 
corticifugal  and  corticipetal  fibers.  The  corticifugal  fibers  are 
very  largely  axones  from  the  pyramids;  the  incoming  fibers  of 
Meynert's  radiations  rise  in  other  parts  of  the  cortex  or  in  gray 
matter  situated  at  a  lower  level.  The  radiating  fibers  belong  to 
the  following  systems,  the  projection,  the  association  and  the 
commissural.  The  radiations  are  distinct  as  far  out  as  the  external 
layer  of  large  pyramids  and  the  line  of  Baillarger,  hence  the  name 
radiary  zone;  but  in  certain  regions  they  are  much  longer  and 
in  some  parts  of  the  temporal  lobe  they  extend  to  the  stratum 
zonale  of  the  first  layer.  In  such  regions  the  line  of  Baillarger 
divides  the  radiary  zone  into  two  parts  and  there  is  no  proper 
supraradiary  zone. 

Association  Fibers  of  Meynert. — ^This  name  is  applied  to  arcuate 
fibers  of  large  diameter  located  in  the  radiary,  the  Baillargic 
and  the  deep  part  of  the  supraradiary  zone.  Owing  to  condens- 
ation they  form  a  distinct  layer  in  the  fissural  walls  and  floor,  but 
are  sparsely  scattered  in  the  crown  of  the  gyrus  (Campbell). 
They  arch  over  the  medullary  projection,  crossing  Meynert's 
radiations  at  right  angles.  The  deeper  ones  appear  to  be  con- 
tinuous with  certain  fibers  in  the  radiations  and  are  probably 
corticipetal  in  direction  (Kaes  and  Campbell).  Meynert's  asso- 
ciation fibers  are  said  by  Vulpius  not  to  be  developed  before  the 
seventeenth  year;  and,  according  to  Kaes,  are  most  abundant  in 
the  highly  developed  parts  of  the  brain. 

Atypical  Cortex. — ^The  decided  variations  from  the  typical 
cortex  are  found  in  the  visual  and  olfactory  areas. 

Visual  Receptive  Center  (Fig.  60). — ^The  cortex  in  the  cuneus 
and  gyrus  lingualis  presents  three  marked  variations  from  typical 
cortex:     i.  The   greatly    accentuated   line   of   Baillarger,    which 


THE    CORTICAL    GRAY    MATTER. 


193 


:>  I  iff    6  /  ■'  ,  ■ 


1<* 


V 


^ 


Fig.  60. — Cell  and  fiber  lamination  in  the  calcarine  region.  Receptive  visual 
•AREA.  (After  A.  W.  Campbell's  "  Histological  Studies  on  the  Localization  of  Cere- 
bral Function."     Published  by  the  Syndics  of  the  Cambridge  University  Press.) 

A.  Shows  fibers  of  occipital  cortex.  B.  Cells  of  same.  z.  Stratum  zonale.  s.  Supra-radiary 
zone.  G.  Line  of  Baillarger  or  Genari.  R.  Radiar>' zone.  i.  Plexiform  layer.  2.  Layerof 
small  pyramids.  3.  Layer  of  medium-sized  pyramids.  4.  External  layer  of  large  stellate 
cells.  5.  Small  stellate  cells.  6.  Layer  of  giant  pyramidal  or  stellate  cells  with  some  small 
pyramids.    7.  Layer  of  fusiform  cells  with  some  medium-sized  pyramids. 


THE    CORTICAL    GRAY    MATTER.  195 

may  be  seen  di\iding  the  cortex  into  two  gray  layers.  This  line 
was  first  seen  and  described  in  the  visual  area  by  Gennari  and, 
ten  years  later,  by  Vicq  d'Azyr.  2.  The  external  layer  of  large 
pyramids  is  replaced  by  a  layer  of  stellate  cells  25/i  in  diameter. 
These  stellate  cells  give  off  three  or  four  strong  processes  which 
appear  to  arborize  in  the  line  of  Baillarger.  They  are  found  in 
the  receptive  and  psychic  visual  areas  but  not  elsewhere  in  the 
cerebral  cortex.  3.  The  internal  layer  of  large  pyramids  is  re- 
placed by  a  conglomerate  made  up  of  three  varieties  of  pyramids. 
From  without  inward  there  are:  First,  small  inverted  pyramids, 
cells  of  Martinotti,  which  extend  their  axones  out  toward  the 
surface.  Second,  the  scattered  giant  pyramids,  25-30//  in  dia- 
meter, arranged  in  a  single  row  and  called  the  solitary  cells  of 
Meynert.  The  axones  of  the  giant  pyramids  probably  pass  into 
the  optic  radiation.     Third,  a  layer  of  medium-sized  pyramids. 

Olfactory  Cortex. — ^All  the  di\isions  of  the  rhinencephalon 
are  here  mentioned,  though  only  a  part  of  them  need  be  described : 
the  olfactory  bulb,  triangle,  parolfactory  area,  anterior  perforated 
substance,  g}Tus  subcallosus,  septum  pellucidum,  gyrus  supra- 
callosus  (longitudinal  striae),  fasciola  cinerea,  fascia  dentata, 
hippocampus,  subiculum  and  uncus.  The  posterior  inferior 
part  of  the  liippocampal  gyrus  and  the  g}Tus  cinguli  are  ordinarily 
included  in  the  rhinencephalon;  but,  according  to  Elliot  Smith, 
they  belong  to  the  neopallium  (Figs.  26,  28  and  62). 

The  cortex  of  the  olfactory  bulb  (Fig.  63)  is  divided  into  five 
layers  as  pictured  by  Barker.  These  five  layers  are  as  follows, 
named  from  the  surface  toward  the  center:  (i)  The  stratum 
nervosum,  composed  of  the  T-branched  fibers  from  the  olfactory 
nerve  and  their  collaterals.  These  fibers  run  nearly  parallel 
with  the  surface  for  some  distance,  then  bend  centrally  and  break 
up  into  their  end-tufts  in  the  second  layer.  (2)  The  stratum 
glomerulosum  is  made  up  of  round  bodies,  called  glomeruli,  which 
are  composed  of  the  end-tufts  of  olfactoiy  nerve  fibers  and  of 
brush-like  dendrites  from  the  spindle  and  mitral  cells  of  the  third 
and  fourth  layers.  The  glomeruh  constitute  the  s}Tiapses  between 
the  first  and  second  olfactory  neurones.  (3)  The  stratum  relic- 
iilare.     This   is   a  network  of   mitral  dendrites  interwoven  ^^•ith 


196  THE    CEREBRUM. 

arborizing  processes  from  the  granules  in  the  fifth  layer  and  the 
branches  of  a  few  endogenous  spindle  cells,  called  the  brush  cells. 
The  mitral  dendrites  are  on  their  way  to  the  glomeruli  in  the 
second  layer.  The  spindle  cells  likewise,  both  large  and  small, 
throw  their  dendritic  processes  down  into  the  stratum  glomeru- 
losum,  where  they  end  in  rich  tufts  or  brushes;  and  their  axones 
penetrate  the  fourth  and  fifth  layers,  enter  into  the  white  sheath 
of  the  bulb  and  thence  are  continued  into  the  olfactory  tract. 
(4)  The  stratum  cellulare,  or  layer  of  mitral  cell-bodies.  The 
mitral  cells  have  large  pyramidal  bodies  with  one  axone  and  rich 
dendritic  processes.  The  latter  arborize  through  the  reticular 
layer  to  the  glomeruli  of  the  second  layer,  where  they  terminate 
in  the  form  of  end-brushes.  The  axones  of  the  mitral  cells  run 
centrally  through  the  granular  layer,  to  which  they  give  off  col- 
laterals, and  then  turn  backward  in  the  white  sheath  and  ulti- 
mately constitute  the  olfactory  tract.  The  white  sheath  incloses 
a  mass  of  cells  derived  from  the  ependymal  lining  of  the  ventricle 
in  the  embyro.  (5)  The  stratum  granule  sum  is  composed  of  a 
thick  layer  of  small  cell-bodies,  "granules,"  whose  processes 
arborize  richly  in  the  granular,  cellular  and  reticular  layers. 
Imbedded  in  the  granular  layer  are  the  medullated  axones  coursing 
toward  the  "white  sheath  and  the  olfactory  tract.  The  function 
of  the  granular  layer  is  not  understood.  The  mitral  and  spindle 
cells  of  the  olfactory  bulb,  it  should  be  carefully  noted,  form  the 
terminal  nucleus  of  the  olfactory  nerves:  the  points  of  contact 
between  them  are  established  in  the  glomeruli;  and  the  axones 
of  the  nucleus  constitute  the  olfactory  tract  and  its  stria,  which 
join  the  bulb  to  the  cerebral  hemisphere  (Fig.  63).  The  lateral 
stria  of  the  olfactory  tract  runs  directly  to  the  uncus,  hence  we 
shall  study  that  region  next. 

The  uncus  and  crown  of  the  hippocampal  gyrus  (Figs.  55,  61 
and  62)  probably  represent  the  greater  part  of  the  lobus  pyra- 
formis  of  osmatic  mammals.  It  constitutes  the  chief  cortical 
center  of  smell.  However  it  is  probable  that  the  subiculum, 
hippocampus,  fascia  dentata,  and  anterior  end  of  the  gyrus  cinguli 
belong  in  the  cortical  area  of  smell,  as  all  showed  arrested  develop- 
ment in  two  cases  of  congenital  absence  of  the  olfactory  bulbs 


THE  CORTICAL  GRAY  MATTER. 


197 


Fig.  61. — Cell  and  fiber  lamination  in  the  uncus  hippocampi  (lobus  pyraformis). 
The  AREA  OF  SMELL.  (After  A.  W.  Campbell's  "Histological  Studies  on  the  Lo- 
calization of  Cerebral  Function.  Published  by  the  Syndics  of  the  Cambridge 
University  Press.) 

A.  Showing  fibers.  B.  Showing  cell-bodies,  z.  Stratum  zonale,  external  medullary 
lamina,  s.  Supraradiary  zone  containing  radiating  filbers.  b.  Line  of  Baillarger.  r. 
Radiary  zone.  i.  Plexiform  layer.  2.  Layer  of  stellate  cells  showing  cell-nests.  3.  Repre- 
sents third  and  fourth  layers  of  typical  cortex,  medium-sized  pyramids  obliquely  placed  and 
stellate  cells;  with  Golgi's  silver  method  shows  tassel-cells.  4.  Fusiform  or  triangular  cells. 
5.  Medium-pyramids.     6.  Fusiform  cells. 


THE    CORTICAL    GRAY    MATTER.  I99 

(Zuckcrkandl).  The  fascia  dentata  is  of  first  im];ortance  accord- 
ing to  Alexander  Hill.  He  calls  attention  to  the  fact  that  the 
Narwhal,  which  has  no  sense  of  smell,  possesses  e\'ery  part  of 
the  hippocampal  region  excepting  the  dentate  fascia  (Campbell). 
The  uncus  comprises  the  whole  anterior  part  of  the  gyrus  hippo- 
campi. In  structure  the  crown  of  the  hippocampal  gyrus  and 
the  uncus  are  nearly  identical.  They  have  only  jive  layers  of 
cells,  (i)  As  already  pointed  out  the  plexiform  layer  is  thick 
and  possesses  a  dense  stratum  zonale,  only  second  to  that  of  the 
subiculum.  (2)  The  place  of  the  small  pyramids  is  usurped  by 
the  ^'olfactory  islets^'  (Calleja)  which  are  curious  nests  of  large 
stellate  cells  (28/1)  interspersed  with  small  nests  of  very  minute 
pyramidal  cells.  (3)  The  tassel-cells  of  Cajal.  Peculiar  pyram- 
idal cells,  with  such  rich  dendritic  arborizations  hanging  from  the 
bases  as  to  resemble  tassels,  are  seen  in  the  place  of  the  medium- 
sized  pyramids.  At  the  line  of  Baillarger  there  are  no  cells;  the 
fourth  layer  of  typical  cortex  is  entirely  wanting.  (4)  The 
stellate  layer  and  internal  layer  of  large  pyramids  are  replaced 
by  a  layer  of  intermixed  fusiform  and  triangular  cells  heavy  with 
Nissl  bodies.     (5)  The  fusiform-cell  layer  is  nearly  typical. 

Nucleus  AmygdalcE  (Fig.  32). — ^In  the  anterior  wall  of  the 
inferior  horn  of  the  lateral  ventricle,  near  the  temporal  pole  and 
dorsal  to  the  uncus  hippocampi,  is  the  amygdala,  a  nucleus  of 
doubtful  classification.  The  amygdala  is  in  part  continuous 
with  the  corpus  striatum  and,  according  to  Campbell,  appears 
on  the  surface  of  the  uncus  as  the  gyrus  semilunaris. 

Cortex  of  the  Lower  Wall  and  Lip  of  the  Hippocampal  Fis- 
sure (Fig.  62). — ^This  is  known  as  the  subiculum.  It  is  especially 
distinguished  for  its  remarkable  stratum  zonale,  which  is  visible 
to  the  naked  eye,  and  for  its  long  radiations,  which  reach  the 
zonal  layer  and  give  the  cortex  a  striated  appearance,  (i)  The 
plexiform  layer  is  almost  wholly  occupied  by  the  stratum  zonale, 
called  here  the  external  medullary  lamina.  (2)  The  layer  of 
olfactory  islets.  The  islets  are  closely  packed  nests  of  minute 
triangular  cells,  5,u  in  diameter,  resembling  those  in  the  uncus. 
(3)  The  stratum  radiatum  occupies  about  three-fourths  of  the 
depth  of  this  cortex.     In  its  deep  part   (the  stratum  lucidum) 


200  THE    CEREBRUM, 

there  are  several  layers  of  medium-sized  pyramids,  arranged  in 
columns.  The  prominent  apical  processes  of  these  pyramids 
collect  in  bundles  and  proceed  outward  to  the  stratum  zonale, 
separating  the  columns  of  pyramids  and  producing  the  striations 
above  mentioned.  As  the  apical  dendrites  approach  the  olfactory 
islets  they  branch  richly.  The  axones  of  the  pyramids  run  straight 
to  the  white  core  of  the  gyrus  or  into  the  alveus.  The  pyramids 
continue  without  interruption  through  the  hippocampus  into 
the  nucleus  of  the  dentate  fascia.  The  alveus,  which  forms  the 
ventricular  surface  of  the  hippocampus,  is  made  up  largely  of  the 
axones  of  these  pyramids;  from  the  alveus  they  proceed  into  the 
crus  of  the  fornix.  (4)  A  few  fusiform  or  stellate  cells  lie  next 
the  alveus.  They  belong  to  the  type  of  Golgi,  the  axone  being 
wonderfully  branched.  In  function  they  are  associative.  It  is 
in  the  region  of  these  associative  neurones  that  the  axones  of  the 
pyramids  bend  and  adjust  themselves  so  as  to  enter  the  alveus 
nearly  parallel  with  its  surface,  hence  the  name  stratum  oriens 
applied  to  it  by  Edinger. 

The  fascia  dental  a  (Fig.  62)  is  a  free  lip  of  cortex  folded  inward 
anterior  to  the  hippocampal  fissure.  It  presents  a  type  of  struc- 
ture, which  is  continued,  forward,  through  the  band  of  Giacomin 
into  the  reflected  part  of  the  uncus;  and  which  extends  backward 
through  the  fasciola  cinerea  into  the  gyrus  supracallosus  (longit- 
udinal striag  of  the  corpus  callosum).  It  is  similar  in  structure 
to  the  subiculum,  the  first  and  the  third  layers  only  present  a 
marked  variation.  The  stratum  zonale  is  not  so  prominent  as 
in  the  subiculum;  and  the  stratum  radiatum  is  entirely  replaced 
by  the  nucleus  fasciae  dentatae.  The  nucleus  is  composed  of  pyra- 
mids, of  polymorphous  and  fusiform  cells  and  their  branches. 
Their  dendrites  radiate  toward  the  stratum  zonale,  their  axones 
proceed  into  the  crus  of  the  fornix.  The  dentate  fascia  is  absent 
in  anosmatic  animals  (A.  Hill). 

Trigonum  Olfaclorium,  Area  Parol factoria  (Brocce),  Gyrus 
Subcallosus  and  Septum  Pellucidum,  and  Substantia  Perforata 
Anterior  (Figs.  26  and  28). — ^These  are  the  parts  into  which  run 
most  of  the  fibers  of  the  medial  and  intermediate  striae  of  the 
olfactory  tract.     They  are  more  conspicuous  in  the  embryo  than 


THE  CORTICAL  GRAY  MATTER. 


20I 


Fig.  62. — Transverse  section  of  the  hippocampal  region.     (.A.fter  Edingcr.) 
a.  Nucleus  of  fascia  dentata. 


THE    CORTICAL    GRAY    MATTER. 


203 


in  the  adult  human  brain.  The  cortex  of  this  whole  region  is 
so  rudimentary  or  vestigial  as  to  rcc|uire  but  brief  description. 
The  plexiform  layer  may  be  identilied.  The  whole  gray  substance 
beneath  that  is  occupied  by  scattered  pyramids  of  medium  size, 
separated  by  strands  of  fibers  belonging  to  the  olfactory  tract  and, 
perhaps,  to  the  cingulum. 


Central  core  01 
ependymal  cells 


5.   S.  granulosur.-. 


4.  S.  cellulare 
3.  S.  reticulare 


2.  S.  glomeru- 
losum 


I.  S.  nervosum 


Nasal  mucous 
membrane 


Olfactory  cell- 
bodies 


Fig.  63.— Chief  elements  of  the  olfactory  bulb.     {Gordinicr  after  Van  Gehuchten.) 


The  cortex  of  the  gyrus  cinguU  (Fig.  28)  is  characterized  by 
an  entire  absence  of  large  fibers  and  large  cells,  by  an  oblique 
and  irregular  direction  of  the  pyramids  and  by  a  most  remarkable 
color  affinity  possessed  by  the  deep  cells.  There  are  only  jour 
cell  layers,  (i)  The  plexiform  presents  a  faint  stratum  zonale, 
but   nothing   characteristic.     (2)  The   layer   of   small    pyramids 


204  THE    CEREBRUM. 

is  ill  defined.  (3)  A  layer  of  medium-sized  pyramids  placed  at 
various  angles  occupies  the  place  of  the  third,  fourth,  fifth  and 
sixth  layers  of  typical  cortex,  (4)  The  layer  of  spindle  cells. 
In  the  spindle-cell  layer  are  found  th.e  remarkable  chromophilous 
cells.  They  are  triangular  or  pyramidal  in  shape  and  have  greater 
affinity  for  stains  than  the  cells  of  any  other  part  of  the  cerebral 
cortex. 

The  claustrum  (Figs.  31  and  42)  is  a  sheet  of  peculiar  gray 
substance  which,  according  to  Meynert,  may  be  classed  as  cortical. 
In  structure  it  resembles  the  seventh  layer  of  typical  cortex, 
being  made  up  of  fusiform  cell-bodies.  The  claustrum  is  a 
vertical  antero-posterior  sheet  placed  medial  to  the  island,  and 
lateral  to  the  external  capsule.  The  surface  in  contact  with  the 
external  capsule  is  smooth,  but  the  external  surface  is  convoluted 
to  coincide  with  the  gyri  insulae.  At  its  lower  border  it  joins  the 
lentiform  nucleus. 

II.     GANGLIONAR  GRAY  MATTER. 

The  substantia  grisea  ganglionaris  is  found  in  the  great  ganglia 
which,  in  their  situation  and  relations,  have  already  been  con- 
sidered. They  should  be  re-studied  in  this  connection.  They 
are  as  follows: 

1.  In  the  hemisphere: 

The    corpus    striatum,   composed   of  the   caudate  and   the 
lentiform  nucleus. 

2.  In  the  inter-brain: 

The  thalamus,  lateral  and  medial  geniculate  bodies,  nucleus 
hypothalamicus  (Luysi)  and  red  nucleus. 

3.  In  the  mid-brain: 

The  superior  and  inferior  quadrigeminal  colliculi,  the  sub- 
stantia  nigra,  and   the   nucleus  lateralis  superior  in  the 
tegmentum. 
The  corpus  striatum  (Figs.  64,  31  and  66)  is  an  ovoid  mass 
of    reddish-gray   matter    containing   pigmented   multipolar    cell- 
bodies  of  various  sizes,  those  of  large  size  being  more  numerous 
in  the  nucleus  lentiformis  than  in  the  nucleus  caudatus.     The 


GANGLIONAR    GRAY    MATTER. 


205 


Fig.  64. — Horizontal  section  of  cerebrum  through  genu  and  below  splenium  of 
corpus  callosum.  Fornix  and  chorioid  tela  turned  back,  to  show  inter-brain 
and  third  ventricle.     (Original.) 

a.  Head  of  caudate  nucleus,  b.  Stria  medullaris  fhalami  (or  pineal  stria.)  c.  Chorioid 
groove,  d.  Trigonum  habenulae.  e.  Pineal  body.  f.  Tail  of  caudate  nucleus,  g.  Tapetum. 
h.  Occipito-thalamic  radiation,  i.  Inferior  longitudinal  fasciculus,  j.  Anterior  horn  of 
lateral  ventricle,  k.  Columna  of  fornix.  1.  Recessus  triangularis,  m.  Anterior  commissure, 
n.  Massa  intermedia  (or  middle  commissure),  o.  Posterior  commissure,  p.  Superior,  quad - 
rigeminal  colliculus.    q.  Posterior  horn  of  lateral  ventricle. 


GANGLIONAR    GRAY    MATTER. 


207 


axones  of  those  cell-bodies  run  both  toward  the  pons  and  toward 
the  cerebral  cortex.  The  corpus  striatum,  therefore,  forms  a 
relay-station  in  an  efferent  conduction  tract  and,  perhaps  a  less 
important  one,  in  an  afferent  tract. 

Of  the  centrifugal  fibers  note  the  following  three  groups: 
(i)  The  cortico-striale  radiation  made  up  of   corticifugal  and 


Caudate  nucleus 

Stria  terminalis 

Pulvinar' 

Brachium  superius 


Inferior 
quadrigeminal 
■■    colliculus 
Medial  genicu- 
late body 


Lateral  genicu- 
late body 


Lateral  stria  of 
oltactory  tract 


Olfactory  bulb. 


Anterior 

perforated 

substance 


Fig.  65. — Dissection  of  brain  to  show  geniculate  bodies,  optic  tract,  nucleus 
amygdalae,  etc.     (After  Morris's  Anatomy.) 

corticipetal  fibers  running  from  and  to  the  equatorial  zone  of 
the  hemisphere.  (2)  The  striato-ihalamic  fibers,  wliich  are  in 
part  crossed  fibers,  pass  through  the  inferior  lamina  of  the  in- 
ternal capsule  and  terminate  in  many  nuclei  of  the  inter-brain, 
mid-brain  and  pons;  some  of  them  pierce  the  superior  lamina 
of  the  capsule.     They  run  to  the  thalamus,  hypothalamus  and 


2o8  THE    CEREBRUM. 

hypothalamic  nucleus  of  both  sides,  the  crossing  fibers  forming 
the  superior  commissure  (Meynert's)  in  the  tuber  cinereum;  to  the 
nucleus  ruber  and  quadrigeminal  colliculi;  and,  through  the 
deep  part  of  the  basis  pedunculi,  to  the  substantia  nigra  and 
nucleus  pontis  (Fig.  70).  The  last  tract  is  the  stratum  intermedium, 
or  the  intermediate  bundle  of  the  basis  pedunculi  (Fig.  68).  (3) 
The  olivary  bundle  (fasciculus  olivaris)  probably  rises  in  the 
globus  pallidus  (or  thalamus)  and  descends  to  the  nucleus  of  the 
olive  in  the  medulla.  In  addition  to  the  above,  it  is  probable 
that  the  fronto-pontal  and  temporo-pontal  tracts  are  relayed  in 
the  corpus  striatum  or  thalamus. 

The  centripetal  fibers  connected  with  the  corpus  striatum 
are  also  numerous,  (i)  The  thalamostriate  fibers,  which  belong 
to  the  common  sensory  path,  rise  partly  in  the  thalamus  and 
partly  from  nuclei  lower  down.  They  run  through  the  frontal 
stalk  and  the  vpntral  stalk  of  the  thalamus  and,  perhaps,  through 
the  parietal  stalk,  and  include  uninterrupted  fibers  of  the  medial 
fillet  and  spino-thalamic  tract  (Fig.  70).  (2)  Fibers  from  the 
globus  pallidus  to  the  posterior  central  cortex  in  the  cortico-striate 
radiation  (the  alpha  and  gamma  bundles  of  Flechsig).  These 
enter  the  parietal  stalk  high  up  in  the  superior  lamina  of  the 
capsule. 

Lesions  of  the  corpus  striatum  affect  the  internal  capsule,  which 
impales  it;  and  may  cause,  if  extensive,  hemiplegia  and  hemian- 
esthesia of  the  opposite  side  of  the  body,  partial  deafness  chiefly 
in  the  opposite  ear  and  hemianopia  due  to  cortical  isolation  of  the 
corresponding  halves  of  both  retinae. 

The  thalamus  (Figs.  64,  66  and  31)  is  made  up  chiefly  of 
gray  matter  containing  multipolar  and  fusiform  cell-bodies.  The 
white  matter  consists  of  the  stratum  zonale  on  its  free  surface  and 
of  the  internal  medullary  lamina.  The  latter  divides  the  gray 
substance. into  nuclei,  of  which  Nissl  has  described  about  twenty. 
They  may  be  grouped  as  follows:  The  medial,  lateral,  anterior, 
nucleus  of  the  pulvinar  and  nucleus  habenulae. 

(i)  The  medial  nucleus  is  joined  to  the  opposite  medial  nucleus 
by  the  massa  intermedia  and  is  continuous  with  the  hypothalamic 
gray  matter  in  the  wall  and  floor  of  the  third  ventricle;  but  the 


GANGLIONAR    GRAY    MATTER. 


209 


r  '-'  ~^~^-ll 

Fig.  66. — Transverse  section  of  the  brain  in  the  line  of  the  pyramidal  tracts,  show- 
ing basal  ganglia,  internal'  capsules,  corpus  callosum,  lateral  and  third  ventric- 
les, etc.     Viewed  from  front.     (Morris's  Anatomy  after  Toldt.) 

a.  Longitudinal  fissure,  b.  Radiation  of  corpus  callosum.  c.  Septum  pellucidum.  d. 
Chorioid  plexus  of  lateral  ventricle,  e.  Corona  radiata.  f.  Column  of  fornix,  g.  Chorioid 
plexus  of  third  ventricle,  h.  Internal  capsule,  i.  Thalamus,  j.  Third  ventricle,  k.  Inter- 
peduncular fossa.  1.  Inferior  horn  of  lateral  ventricle,  m.  Cerebral  peduncle,  n.  Brachitmi 
pontis.  o.  Longitudinal  pyramidal  fasciculi  of  pons.  p.  Cerebellum,  q.  Deep  fibers  of 
pons.  r.  Pyramid,  s.  Superior  frontal  go'rus.  t.  Body  of  corpus  callosum.  u.  Anterior 
horn  of  lateral  ventricle,  v.  Head  of  caudate  nucleus,  w.  Radiation  of  corpus  striatum. 
X.  Putamen.  y.  External  capsule,  z.  Insula,  aa.  Claustrum.  bb.  Globus  pallidus.  cc. 
Optic  tract,  dd.  Corpus  mammillare.  ee.  Oculo-motor  nerve,  ff.  Trigeminal  nerve,  gg. 
Facial  and  acoustic  nerves,  hh.  Flocculus,  ii.  Glossopharyngeal  nerve,  jj.  Vagus  nerve, 
kk.  Inferior  olivary  nucleus.     11.  Decussation  of  pjTamids. 


14 


GANGLIONAR    GRAY    MATTER.  211 

internal  medullary  lamina  separates  it  from  the  other  nuclei  of 
the  same  thalamus.  It  gives  origin  to  a  part  of  the  \-entral  stalk 
of  the  thalamus.  According  to  Bechterew  it  probably  gives 
rise  to  some  descending  fibers  that  run  down  the  cord.  (Jas.  S. 
Collier  has  traced  thalamo-spinal  fibers  in  the  cat  down  the  lateral 
column  of  the  cord.) 

(2)  The  lateral  nucleus  is  the  largest.  It  extends  from  superior 
to  inferior  surface  the  entire  length  of  the  thalamus,  and  includes 
the  center  median  (Luysi)  and  the  arcuate  nucleus,  both  of  which 
fuse  with  it  posteriorly.  It  also  fuses  with  the  nucleus  of  the 
pulvinar.  It  forms  the  terminal  nucleus  for  the  larger  part  of 
the  tegmental  fibers,  especially  of  the  medial  fillet,  the  spino-thala- 
mic  tract,  a  part  of  the  medial  longitudinal  bundle  and  the  brach- 
ium  conjunctivum  of  the  cerebellum;  and  it  constitutes  the  nucleus 
of  origin  for  most  of  the  fibers  of  the  cortical  fillet.  Destruction 
of  this  nucleus  interrupts  the  common  sensory  path,  and  causes 
anesthesia  and  ataxia  of  the  opposite  side. 

(3)  The  nucleus  of  the  anterior  tubercle  (Fig.  44)  receives  the' 
fasciculus  thalamo-mammillaris  (Vicq  d'Azyri)  from  the  corpus 
mammillare  and  is  thus  connected  vdth  the  columna  of  the  for- 
nix (Fig.  66). 

(4)  The  nucleus  0}  the  pulvinar  (Fig.  44)  is  an  important  one. 
It  receives  about  twenty  per  cent,  of  the  optic  fibers  and  gives 
rise  to  a  corresponding  number  of  the  corticipetal  fibers  in  the 
optic,  or  occipito-thalamic  radiation;  hence,  a  lesion  of  the  pulvinar 
impairs  vision.     It  is  continuous  with  the  lateral  nucleus. 

(5)  The  nucleus  of  the  habenula  belongs  to  the  epithalamus 
(Fig.  64).  It  lies  beneath  the  trigonum  habenulte.  It  receives 
fibers  from  the  rhinencephalon  through  the  medullary  stria  of 
the  thalamus,  and  originates  a  bundle  of  fibers,  the  fasciculus 
retroflexus  (Meynerti),  w^hich  may  be  traced  back  through  the 
tegmentum  to  the  interpeduncular  ganghon  in  the  substantia 
nigra.  Beyond  this,  connections  are  probably  established  with 
the  motor  nuclei  of  cerebral  nerves. 

The  white  matter  of  the  thalamus  includes,  first,  the  stratum 
zonale  of  the  superior  surface,  which  is  deriA-ed  from  the  occipito- 
thalamic  radiation  and  the  lateral  root  of  the  optic  tract;  and, 


212  THE    CEREBRUM. 

second,  the  interior  fibers,  a  part  of  which  form  the  internal  medul- 
lary lamina.  Into  the  thalamus  enter  the  medial  fillet,  the  spino- 
thalamic tract,  a  small  part  of  the  medial  longitudinal  bundle, 
the  brachium  conjunctivum  cerebelli  and  perhaps  some  other 
tegmental  fibers,  all  carrying  common  sensory  impulses;  they  end 
chiefly  in  the  lateral  nucleus,  whence  the  cortical  fillet  proceeds 
to  the  sensory  area  of  the  cerebral  cortex.  The  thalamus  also 
receives  fibers  from  the  special  sense  paths,  from  the  optic, 
auditory,  olfactory,  and  probably  the  gustatory  (?),  and  gives 
rise  to  fibers  that  continue  in  those  paths  to  the  special  sense  areas 
of  the  cortex  or  as,  in  the  case  of  the  olfactory,  to  reflex  centers. 
It  is  also  known  that  the  thalamus  is  entered  by  a  considerable 
number  of  corticifugal  fibers,  especially  through  the  occipito- 
thalamic  and  temporo- thalamic  radiations.  The  several  bundles 
of  thalamic  fibers  are  as  follows: 

(i)  The  columna  of  the  fornix,  having  pierced  the  thalamus, 
descends  to  the  corpus  mammillare  and  terminates  in  its  medial 
nucleus,  whence  the  bundle  of  Vicq  d'Azyr,  the  thalamo-mammil- 
lary  bundle,  rises  and  ascends  to  the  thalamus.  It  ends  in  the 
anterior  nucleus. 

(2)  The  stria  medullaris  thalami  (Fig.  64)  from  the  hippocampus 
and  from  the  region  of  the  olfactory  triangle,  terminates  in  the 
nucleus  habenulas  and  from  this  nucleus  the  fasciculus  retrofiexus 
originates  and  descends  to  the  interpeduncular  ganglion.  Both 
"one"  and  "two"  belong  to  the  olfactory  paths. 

(3)  From  the  lateral  surface  of  the  thalamus  issue  two  groups 
of  fibers  which  rise  chiefly  in  the  lateral  nucleus.  They  are 
common  sensory  in  function :  (a)  The  inferior  one  is  the  ventral 
stalk  (ansa  peduncularis)  (Fig.  70),  which  rises  from  the  medial 
and  lateral  nuclei  and  is  in  part  relayed  in  the  lentiform  nucleus 
under  which  it  passes  toward  its  destination.  It  proceeds  through 
the  inferior  lamina  of  the  internal  capsule  and  contributes  fibers 
to  both  the  medullary  laminae  of  the  lentiform  nucleus  and  to  the 
external  capsule.  Underneath  the  lentiform  nucleus  the  ventral 
stalk  is  divided  into  two  horizontal  laminae  by  a  thin  sheet  of  gray 
substance.  The  upper  lamina,  the  ansa  lenticularis,  is  inter- 
mingled with  the  striato-thalamic  fibers  and  enters  into  the  lenti- 


GANGLIONAR  GRAY  MATTER. 


213 


LATERAL  GENIC- 
ULATE BODY 


Fig.  67. — The  optic  path.     {Original.) 


GANGLIONAR    GRAY    MATTER. 


2'5 


form  nucleus,  where  it  probably  terminates;  but  the  conduction 
path  to  which  it  belongs  is  continued  to  the  upper  third  of  the 
posterior  central  and  tlie  paracentral  gyri  by  the  al]jha  and  gamma 
bundles  of  Flechsig.  The  lower  lamina  of  the  ventral  stalk,  the 
inferior  peduncle,  runs  principally  into  the  external  capsule  medial 
to  the  claustrum,  but  a  part  of  it  dips  under  the  claustrum.  It 
terminates  in  the  temporal  lobe  and  the  island,     (b)  The  superior 


Fig.  68. — Section  of  the  mid-brain  through  superior  coUiculi  and  the  apparent 
origin  of  the  oculomotor  nerve.     {Original.) 

a.  Sulcus  latemlis  of  mid-brain,  b.  Red  nucleus,  c.  Medial  longitudinal  bundle,  d.  Oculo- 
motor nucleus,  e.  Stratum  griseum  centrale.  f.  Colliculus  superior  of  corpora  quadrigemina. 
g.  Formatio  reticularis,  h.  Medial  fillet,  i.  Medial  geniculate  body.  j.  Optic  tract,  k.  Basis 
pedunculi.  1.  Dorsal  tegmental  decussation  (Meynerti).  m.  Ventral  tegmental  decussation 
(Foreli).  n.  Fossa  interpeduncularis.  o.  Substantia  nigra,  p.  Fronto-pontal  tract,  q.  3d.  N. 
r.  Pyramidal  tract,    s.  Intermediate  tract,    t.  Temporo-pontal  tract. 


group  of  libers  that  issues  from  the  lateral  surface  of  the  thala- 
mus is  the  parietal  stalk  (Fig.  70).  It  rises  from  the  lateral  nucleus 
arid  traverses  the  superior  lamina  of  the  internal  capsule.  To 
a  slight  extent  it  is  probably  relayed  in  the  lentiform  nucleus. 
It  terminates  in  the  posterior  central  gyrus  and  in  the  paracentral 
lobule.  This  parietal  stalk,  in  the  upper  limits  of  the  internal 
capsule,  contains  nearly  all  of  the  common  sensory  fibers  going 


2l6 


THE    CEREBRUM. 


to  the  cortex.  Flechsig  has  found  that  in  development  it  is  built 
up  of  six  distinct  strands  of  fibers,  which  receive  their  medullary 
sheaths  one  after  the  other;  and  he  names  the  bundles,  according 
to  the  order  of  their  medullation,  after  the  first  six  letters  of  the 
Greek  alphabet  (see  page  232). 

.  (4)  The  frontal  stalk  (Fig.  70)  streams  from  the  anterior  end 
of  the  lateral  nucleus  via  the  frontal  part  of  the  internal  capsule. 
Its  fibers  end  in  the  corpus  striatum  and  the  frontal  cortex.     In 


Fig.  69. 


-Section  of  the  mid-brain  cutting  the  inferior  colliculi  of  the  corpora 
quadrigemina.     (Original. ) 


a.  Sulcus  lateralis,  b.  Formatio  reticularis,  c.  Medial  longitudinal  bundle,  d.  Nucleus 
of  colliculus  inferior,  e.  Aqueductus  cerebri,  f.  Rubro-spinal  tract,  g.  Lateral  fillet,  h. 
Medial  filliet.  i.  Basis  pedunculi.  j.  Location  of  anterior  longitudinal  bundle,  k.  Interpedun- 
cular fossa.    1.  Substantia  nigra,     m.  Decussation  of  brachia  conjunctiva. 


the  globus  pallidus  they  are  probably  relayed  to  the  somaesthetic 
cortex. 

The  ventral,  parietal  and  frontal  stalks  of  the  thalamus  con- 
stitute the  cortical  fillet;  the  parietal  stalk,  high  up,  contains  nearly 
all  the  common  sensory  corticipetal  fibers  and,  alone,  is  often 
called  cortical  fillet.  The  cortical  fillet  carries  common  sensations 
received  from  the  medial  fillet,  the  spino-thalamic  tract,  the 
medial    longitudinal    bundle    and    the    brachium    conjunctivum 


GANGLIONAR  GRAY  MATTER.  21 7 

cercbclli,  up  to  the  somaesthetic  area  (Fig.  54).  Interruption  of 
the  cortical  fillet  stops  all  common  sensory  impulses — tactile,  pain 
and  temperature  impulses,  and  impulses  of  the  muscular  sense. 

(5)  Radiatio  Occipito-ihalamica  (Gratioleti). — ^A  large  pencil  of 
fibers,  the  optic,  or  occipito-thalamic  radiation  (Fig.  70)  passes 
from  the  lateral  geniculate  body  and  the  pulvinar  through  the  in- 
ternal capsule  to  the  visual  centers  in  the  occipital  lobe.  A  num- 
ber of  fibers  in  the  occipito-thalamic  radiation  are  corticifugal  and 
end  in  the  superior  quadrigeminal  colliculus,  though  many  are 
probably  relayed  in  the  thalamus  and  lateral  geniculate  body. 
Destructive  lesion  of  the  occipito-thalamic  radiation  of  either  side 
produces  hemianopia  and  atrophy  of  the  same  side  of  both  retinae. 

(6)  Acustic  Radiation  or  Radiatio  T em poro -thalamic a  (Fig. 
70). — ^Another  pencil  of  fibers  radiates  from  the  region  of  the 
medial  geniculate  body  through  the  internal  capsule  to  the  audi- 
tory area  in  the  temporal  lobe.  It  constitutes  the  temporo- 
thalamic  radiation.  Its  fibers  are  also  in  part  corticifugal  in 
direction.  If  the  temporo-thalamic  radiation  be  destroyed  the 
result  is  partial  deafness  affecting  chiefly  the  opposite  ear. 

According  to  von  Bechterew  certain  lesions  in  the  thalamus  have 
been  accompanied  by  loss  of  facial  movements  expressing  emotion. 

The  red  nucleus  {nucleus  ruber)  of  the  tegmentum  is  situated 
beneath  the  thalamus  (Figs.  42  and  46).  It  is  a  relay-station 
in  the  indirect  sensory  tract,  receiving  the  opposite  brachium 
conjunctivum  cerebelli  and,  by  its  axones,  continuing  the  tract 
to  the  thalamus  and  somaesthetic  cortex.  It  also  receives  efferent 
axones  from  the  cerebral  cortex  (Beevor  and  Horsley)  and  gives 
origin  to  two  bundles:  (a)  One  centrifugal  bundle  of  axones, 
(the  rubro-spinal  tract),  after  crossing  over  in  the  ventral  decussa- 
tion of  the  tegmentum  (Forel's)  descends,  first,  with  the  medial 
portion  of  the  lateral  fillet;  second,  through  the  lateral  area  of  the 
medulla,  and,  third,  through  the  lateral  part  of  the  spinal  cord. 
Gradually  diminishing,  it  disappears  at  the  first  lumbar  segment. 
It  ends  in  the  lateral  columna  and  center  of  the  gray  crescent  of 
the  spinal  cord,  (b)  The  red  nucleus  also  sends  a  bundle  of 
axones  through  the  opposite  brachium  conjunctivum  of  the  cere- 
bellum to  the  nucleus  dcntatus. 


2l8  THE    CEREBRUM. 

The  nucleus  hypothalamicus  (Luysi)  (Figs.  30  and  42)  is  a 
pigmented  bi-convex  mass  of  gray  matter  placed  ventro-lateral 
to  the  red  nucleus,  and  between  it  and  the  basis  pedunculi.  It 
is  separated  from  the  red  nucleus  by  the  zona  incerta.  It  con- 
stitutes an  important  relay  for  certain  corticipetal  fibers  of  the 
tegmentum  and  gives  origin  to  others  belonging  to  the  cortical 
fillet.  Certain  descending  fibers  from  the  striate  body  terminate 
in  this  nucleus.  The  latter  run  through  the  tuber  cinereum, 
just  above  the  posterior  border  of  the  optic  chiasma,  and  form 
the  commissura  superior  (Meynerti),  Gudden's  commissure  being 
called  the  commissura  inferior. 

Metathalamus. — ^The  metathalamus  is  made  up  of  two  ganglia 
at  the  posterior  end  of  the  thalamus,  called  the  geniculate  bodies 
(Fig.  <55).  The  lateral  geniculate  body  {corpus  geniculatum 
laterale)  contains  pigmented  multipolar  cells,  which  receive  80 
per  cent,  of  the  optic  fibers  in  the  corresponding  tract  and  give 
origin  to  a  like  per  cent,  of  the  corticipetal  fibers  in  the  occipito- 
thalamic  radiation;  and,  also,  receive  corticifugal  fibers  from  the 
same  radiation  and  originate  a  part  of  the  brachium  superius. 
The  latter  are  reflex  in  function.  As  the  dark  cell-bodies  are 
arranged  in  layers  separated  by  laminae  of  fibers,  the  body  has  a 
stratified  appearance.  The  medial  geniculate  body  {corpus 
geniculatum  mediale)  is  gray  in  color.  Placed  at  the  end  of  the 
medial  root  of  the  optic  tract,  it  would  at  first  appear  to  be  con- 
cerned in  vision;  but  it  is  not  visual  in  function.  Moreover,  it  is 
a  very  important  station  in  the  auditory  path.  The  medial  optic 
root  is  merely  Gudden's  commissure,  the  fibers  of  which  are 
supposed  to  rise  in  the  medial  geniculate  body.  This  body 
contains  chiefly  fusiform  cell-bodies  which,  in  addition  to  their 
connection  with  the  inferior  commissure  (of  Gudden),  receive 
the  end-tufts  of  fibers  in  the  brachium  inferius  and  send  their 
axones  through  the  acustic,  or  tempoto-thalamic  radiation  to  the 
auditory  cortex;  the  cells  also  receive  corticifugal  fibers  through 
the  temporo-thalamic  radiation  and,  probably,  shoot  some  of 
their  axones  backward  through  the  brachium  inferius  to  the 
corpora  quadrigemina.     The  latter  are  reflex  in  function. 

Ablation  of  the  lateral  geniculate  body  interrupts  the  visual 


GANGLIONAR    GRAY    MATTER.  219 

path,  destruction  of  the  medial  genicidate  breaks  the  auditory 
path. 

The  superior  colliculi  of  the  corpora  quadrigemina  (Figs. 
65  and  68)  represent  the  optic  lobes  of  birds,  fishes  and  reptiles. 
They  contain  the  center  of  optic  reflexes.  In  being  stratified, 
they  bear  some  resemblance  to  the  lateral  geniculate  bodies. 
They  possess  three  white  and  two  gray  layers:  (i)  The  stratum 
zonale  (stratum  album  superficiale)  is  a  layer  of  white  matter 
on  the  surface.  This  invests  the  laminated  stratum  griseum, 
which  forms  the  deep  part  of  the  colliculus  and  comprises  two 
gray  and  two  white  layers:  (2)  The  stratum  griseum  super- 
ficiale is  composed  of  small  multipolar  cells.  (3)  The  stratum 
album  medium  is  a  layer  of  fibers  separating  the  small  from  the 
large  multipolar  cells.  (4)  The  large  cells  make  up  the  stratum 
griseum  profundum,  underneath  which  is  another  layer  of  fibers. 
(5)  The  stratum  album  profundum.  The  fibers  of  the  superficial, 
middle  and  deep  strata  comprise,  first,  those  that  enter  the  collic- 
ulus through  the  optic  tract  and  radiation,  through  the  superior 
and  a  part  of  the  lateral  fillet,  the  striato-thalamic  tract  and  the 
spino-thalamic  tract;  and,  second,  those  that  take  origin  in  the 
colliculus  and  leave  it  through  the  brachium  superius  or  the 
anterior  longitudinal  bundle.  Of  the  fibers  originating  in  the 
superior  colliculus  and  running  through  the  brachium  superius 
it  is  supposed  that  some  go  as  far  as  the  retina;  probably  others 
enter  the  cortical  fillet. 

The  anterior  longitudinal  bundle  is  made  up  of  efferent  axones 
of  the  cell-bodies  in  the  superior  colHculus.  It  crosses  at  once 
through  the  dorsal  tegmental  decussation  (Fig.  68)  and  descends 
ventro-lateral  to  the  opposite  medial  longitudinal  bundle,  to  the 
anterior  columna  of  gray  matter  in  the  spinal  cord.  Its  fibers 
end  largelv  in  the  nuclei  of  the  third,  fourth  and  sixth  cerebral 
nerves  and  in  the  cervical  enlargement  of  the  spinal  cord;  but 
perhaps  others  enter  the  remaining  nuclei  of  motor  cerebral 
nerves,  and  a  few  fibers  of  the  tract  have  been  traced  as  low  as 
the  lumbar  region.  This  bundle  is  the  great  optic  reflex  tract. 
The  fibers  to  the  nuclei  of  the  third,  fourth  and  sixth  cerebral 
nerves  brins:  about  the  reflex  movements  of  the  eveball,  contraction 


220  THE    CEREBRUM. 

of  the  pupil  and  accommodation  to  distance;  while  those  fibers 
which  end  in  the  gray  substance  of  the  lower  part  of  the  cervical 
enlargement  of  the  spinal  cord,  called  the  cilio-spinal  center, 
through  the  white  rami  communicantes  and  cervical  sympathetic, 
produce  dilatation  of  the  pupil.  The  latter  constitute  the  pupillo- 
dilator  tract. 

Destructive  lesions  affecting  the  superior  quadrigeminal  collic- 
uli  produce  loss  of  reflex  movement  of  the  eyeballs,  loss  of  pupillary 
reflex  and  loss  of  accommodation. 

The  inferior  coUiculi  of  the  corpora  quadrigemina  form 
a  relay  in  the  auditory  path  (Figs.  65  and  69).  They  are  made 
up  of  a  white  stratum  zonale,  whose  fibers  are  continuous  chiefly 
with  the  lateral  fillet  and  brachium  inferius,  and  of  a  deep  gray 
mass,  the  nucleus  colliculi  iuferioris,  which  is  composed  of  small 
multipolar  cell-bodies  in  a  network  of  fibers.  The  nuclei  of  the 
two  eminences  fuse  in  the  median  plane.  In  the  nuclei  end  a 
considerable  number  of  fibers  belonging  to  both  lateral  fillets, 
but  most  of  them  belong  to  that  of  the  same  side;  and  from  them 
proceed  axones  of  the  auditory  paths  through  the  brachia  inferiora 
to  the  medial  geniculate  bodies.  A  few  fibers  of  the  spino-thala- 
mic  tract  also  end  in  the  inferior  colliculus.  Again  this  coUiculus 
receives  a  small  bundle  of  the  striato-thalamic  fibers  and,  probably, 
corticifugal  fibers  of  the  temporo-thalamic  radiation. 

Though  the  greater  part  of  the  lateral  fillet  passes  by  the 
inferior  colliculus  without  relay,  a  lesion  in  this  body  is  apt  to 
involve  the  entire  bundle  and  cause  almost  complete  deafness 
in  the  opposite  ear. 

Nucleus  Lateralis  Superior  (Fig.  68). — ^In  the  reticular  for- 
mation of  the  tegmentum  at  the  level  of  the  superior  quadrigeminal 
colliculus  is  the  nucleus  lateralis  superior.  It  contains  large 
multipolar  cell-bodies.  The  nucleus  forms  a  relay  both  for 
ascending  and  descending  fibers  of  the  formatio  reticularis. 
According  to  Tschermak,  a  small  fasciculus  runs  from  this  nucleus 
into  the  medial  longitudinal  bundle  where  it  divides  T-like;  and 
its  descending  fibers  run  down  through  the  anterior  fasciculus 
proprius  of  the  cord  (Barker).  The  spino- thalamic  tract  prob- 
ably undergoes  a  partial  relay  in  the  superior  lateral  nucleus. 


CENTRAL,    OR    VENTRICULAR    GRAY    MATTER.  221 

Substantia  Nigra  (Figs.  66,  67,  68  and  69). — The  small  pig- 
mented multipolar  cell-bodies  which  make  up  the  substantia 
nigra  form,  -first,  a  terminal  nucleus  for  certain  fibers  of  the  medial 
fillet  and  a  nucleus  of  origin  for  other  fibers  which  continue  in 
that  tract  (Barker);  and,  second,  a  terminal  station  for  the  fas- 
ciculus retroflexus  (Meynerti)  and  a  relay  for  the  intermediate 
tract  from  the  corpus  striatum.  Beyond  this  terminal  station  the 
efferent  tracts  are  probably  continued,  but  with  the  exception  of 
the  intermediate  tract  they  have  not  been  traced.  The  inter- 
mediate tract  is  relayed  to  the  nucleus  pontis. 

III.  CENTRAL,  OR  VENTRICULAR  GRAY  MATTER. 

It  is  located  (i)  in  the  floor  and  walls  of  the  third  ventricle, 
the  hypothalamus;  (2)  in  the  middle  commissure  of  that  ven- 
tricle, the  mass  a  intermedia;  and  (3)  around  the  cerebral  aqueduct, 
the  stratum  griseum  centrale. 

(i)  The  Hypothalamus,  Pars  Optica. — ^The  lamina  cinerea 
terminalis  and  the  tuber  cinereum  (Figs.  21  and  27)  form  a  sheet 
of  gray  substance  that  connects  the  inferior  and  medial  surfaces 
of  the  cerebral  hemispheres  and  may  be  called  their  inferior 
gray  commissure.  The  optic  chiasma  is  white  matter,  and  the 
hypophysis  is  not  composed  of  nerve  tissue  at  all  and,  therefore, 
neither  one  need  be  described  in  this  place.  From  the  floor  of 
the  third  ventricle  the  gray  matter  extends  laterally  beneath  the 
thalamus,  and  is  continuous  -^ith  the  anterior  perforated  sub- 
stance. The  gray  matter  of  the  floor  also  extends  up  to  the  sulcus 
hypothalamicus  on  the  medial  surface  of  the  thalamus.  The 
inferior  gray  commissure  receives  eft"erent  fibers  from  the  corpus 
striatum  of  both  sides.  Some  of  these  fibers  form  a  commissure 
just  above  that  of  Gudden;  hence,  it  is  called  the  commissura 
superior  (Meynerti)  to  distinguish  it  from  the  commissura  inferior 
(Guddeni)  in  the  optic  chiasma.  The  fibers  of  ^leynert's  com- 
missure cross  through  the  tuber  cinereum. 

Hypothalamus,  Pars  Mammillaris  (Figs.  26  and  46). — ^The 
corpora  mammillaria  (albicantia),  though  composed  of  fornix 
fibers  on  the  surface,  contain  in  the  interior  two  nuclei,  the  medial 
and  lateral.     The  medial  nucleus  is  the  larger  of  the  two.     It 


222  THE    CEREBRUM. 

receives  the  end-tufts  of  the  fibers  in  the  columna  of  the  fornix 
and  gives  origin  to  the  fasciculus  mammillaris  princeps.  The 
latter  bifurcates,  sending  one  branch,  the  thalamo-mammillary 
bundle  (of  Vicq  d'Azyr),  up  to  the  anterior  nucleus  of  the  thala- 
mus and  the  other  branch,  the  fasciculus  pedunculo-mammil- 
laris,  backward  into  the  tegmentum.  The  fasciculus  thalamo- 
mammillaris  (Vicq  d'Azyri)  connects  the  fornix  with  the  thalamus. 
The  tegmental  part  of  the  pedunculo-mammillary  bundle  has 
been  traced,  in  the  mouse  by  Cajal,  dovmward  to  the  lower  part 
of  the  pons,  running  anterior  to  the  medial  longitudinal  bundle 
(Barker).  The  small  lateral  nucleus  of  the  corpus  mammillare 
gives  origin  to  the  basilar  part  of  the  pedunculo-mammillary 
bundle,  which  according  to  Flechsig  ends  in  the  substantia  grisea 
centrale  of  the  mid-brain  and  is  thence  connected  with  the  motor 
nerve-nuclei  and  the  automatic  centers  of  the  medulla  (Barker). 
Through  the  fornix,  the  stria  medullaris  thalami  and  the  fascic- 
ulus retroflexus,  and  through  the  fornix  and  the  pedunculo- 
mammillary  bundles  the  reflex  connections  of  the  olfactory  nerve 
are  in  part  established. 

'  (2)  The  massa  intermedia  {the  middle  commissure,  Figs.  27 
and  64)  joins  the  medial  nuclei  of  the  thalami.  It  is  formed, 
when  present,  by  the  approximation  and  fusion  of .  the  thalami 
in  the  second  month  of  embryonic  life.  It  is  occasionally  absent. 
In  the  massa  intermedia  are  cell-bodies  and  transverse  fibers. 
The  latter .  appear  to  be  loops  which  reach  only  to  the  median 
line;  at  least  many  of  the  fibers  do  not  cross  to  the  opposite  side. 
It  is  not  a  commissure  in  the  ordinary  sense  of  that  term. 

(3)  The  stratum  griseum  centrale  of  the  mid-brain  (Figs. 
46,  68  and  69)  surrounds  the  cerebral  aqueduct  (Sylvii).  This 
gray  matter  begins  in  the  lateral  wall  of  the  third  ventricle.  It 
extends  through  the  mjd-brain  and  is  continuous  with  the  gray 
substance  in  the  floor  of  the  fourth  ventricle.  Besides  the  nuclei 
of  the  third,  fourth  and  a  part  of  the  fifth  cerebral  nerves,  it  con- 
tains scattered  cell-bodies  of  variable  size  and  shape  which  give 
origin  to  the  true  commissural  fibers  of  the  posterior  commissure. 
According  to  Flechsig  this  central  gray  substance  receives  the 
basilar  part  of  the  pedunculo-mammillary  bundles  and  probably 


CENTRAL,    OR    VENTRICULAR    GRAY    MATTER.  223 

gives  origin  to  libers  that  descend  to  the  motor  nuclei  of  the  pons 
and  the  medulla. 

Oculomotor  Nucleus  (Figs.  45  and  68). — ^The  nucleus  of  the 
third  cerebral  nerve  (nucleus  nervi  oculomotorii)  is  an  elongated 
mass  of  gray  substance  in  the  ventral  part  of  the  stratum  griseum 
centrale,  which  extends  from  the  lateral  wall  of  the  third  ventricle 
down  to  the  level  of  the  transverse  groove  between  the  quadri- 
geminal  colliculi.  The  nuclei  are  placed  somewhat  obhquely; 
at  the  lower  end  they  fuse  in  the  median  plane.  According  to 
Perha,  seven  distinct  cell-nests  are  found  in  each  nucleus;  and 
nest  fifteen  occupies  the  area  of  fusion  and  is  common  to  both 
nerves.  The  greater  number  of  axones  of  this  nucleus  run  jor- 
ward  into  the  nerve  of  the  same  side;  but  those  from  the  median 
nest  go  into  both  nerves,  and  a  small  bundle-  from  each  nucleus 
descends  wiih  the  medial  longitudinal  bundle  to  the  coUiculus 
faciahs,  where  it  joins  the  facial  nerve  and  through  that  nerve 
supplies  the  muscles  of  facial  expression  above  the  orbit. 

Trochlear  Nucleus  (Fig.  69). — ^The  nucleus  ner\i  trochlearis 
is  a  small  oval  mass  of  cell-bodies  situated  anterior  to  the  inferior 
coUiculus  of  the  corpora  quadrigemina.  It  is  in  the  ventral 
part  of  the  stratum  griseum  centrale  like  the  oculomotor  nucleus. 
Unhke  the  third,  the  axones  from  the  nucleus  of  the  fourth  cerebral 
nerve  run  backward  and  issue  from  the  posterior  surface  of  the 
mid-brain  at  the  isthmus;  they  are  pecuhar  also,  in  that  the  axones 
decussate  before  their  emergence  (Fig.  65). 

The  nuclei  of  the  oculomotor  and  trochlear  nerves  receive 
fibers  from  the  cerebral  cortex  through  the  pyramidal  tract  and 
other  motor  tracts  of  the  internal  capsule  and  thus  obtain  their 
voluntary'  motor  and  inhibitor}'  impulses.  It  is  probable  also 
that  the  third  nucleus  receives  fibers,  through  the  medial  longit- 
udinal bundle,  from  the  opposite  abducent  nucleus,  and  that 
the  part  of  the  nucleus  which  receives  these  fibers  suppHes  the 
internal  rectus  muscle  of  the  eye.  For  the  purpose  oj  refiex  both 
the  oculomotor  and  trochlear  nuclei  receive  fibers  from  the  ante- 
rior and  medial  longitudinal  bundles,  from  the  pedunculo-mam- 
millary  bundles  (?)  and,  perhaps,  from  the  cerebellum  through 
the  brachia  conjunctiva. 


224  THE    CEREBRUM. 

Trigeminal  nucleus  of  the  mid-brain  is  a  very  small  nucleus 
situated  in  the  extreme  lateral  part  of  the  central  gray  matter. 
It  is  continuous  with  the  pontine  nucleus  of  the  fifth,  located 
under  the  locus  caeruleus,  and  is  merely  the  superior  end  of  the 
motor  nucleus  of  the  trigeminal.  It  gives  origin  to  the  descend- 
ing root  of  the  fifth  nerve,  which  descends  to  the  pons  and  there 
joins  the  main  motor  root.  In  its  course  downward  the  mesen- 
cephalic root  runs  between  the  central  gray  matter  and  the  bra- 
chium  conjunctivum  cerebelli. 

Lesions  of  these  cerebral  nerve  nuclei  are  apt  to  involve  the 
tegmentum.  If  so,  the  result  is  paralysis  of  the  nerves  on  the 
same  side  and  hemianaesthesia,  hemiataxia,  loss  of  taste  (?)  and 
deafness  on  the  opposite  side. 

The  white  matter  of  the  cerebrum  is  composed,  in  the 
adult  condition,  of  medullated  fibers;  the  medullation  begins  in 
the  ninth  month,  in  utero,  and  is  continued  for  a  considerable 
time  after  birth  (Flechsig).  Within  the  cortical  substance  the 
myehn  sheaths  continue  to  be  laid  down  until  late  in  life  (Kaes,  Mc- 
Murrich).     The  cerebral  fibers  form  three  definite  systems: 

1.  Projection,   or  peduncular  fibers. 

2.  Transverse,   or  commissural   fibers. 

3.  Association  fibers. 

I.     PROJECTION  FIBERS. 

The  projection  fibers  are  connected  only  with  the  motor  and 
sensory  areas  of  the  cerebral  cortex  and  are,  therefore,  motor  and 
sensory  in  function  (Figs.  54  and  55).  Where  they  are  present 
they  are  continuous  with  Meynert's  radiations.  They  are  com- 
posed, first,  of  the  medullated  axones  of  the  pyramids  and  the 
polymorphous  neurones;  these  descend  from  the  cerebral  cortex, 
are  motor  in  function,  or  corticifugal,  and  constitute  the  upper 
motor  segment ;  and,  second,  they  comprise  the  medullated  axones 
of  neurones  whose  cell-bodies  are  situated  in  gray  matter  below 
the  cerebral  cortex;  these  axones  ascend  to  the  cortex  and  are 
sensory  in  function,  or  corticipetal.  The  projection  fibers  run 
from  cerebral  cortex  through  the   corona  radiata,   the  internal 


PROJECTION    FIBERS.  22$ 

capsule  and  ihc  mid-brain,  and  vice  versa  (Figs.  30  and  42). 
They  connect  the  cortex,  directly  or  indirectly,  with  all  parts 
of  the  body,  throwing  or  projecting  a  picture  of  every  part  and 
organ  upon  the  cerebral  cortex.  Many  of  the  fibers  are  inter- 
rupted in  the  basal  ganglia,  especially  of  the  corticipctal  fibers. 
Within  the  hemisphere  all  projection  fibers  run  through  one 
great  sheet,  the  internal  capsule,  with  the  exception  of  the  olfactory; 
but  in  the  mid-brain,  they  are  separated  into  two  great  groups — 
the  basis  pedunculi  and  the  tegmentum,  the  substantia  nigra 
intervening. 

CORTICIFUGAL,  OR  MOTOR  PROJECTION  FIBERS. 

The  most  important  tracts  of  corticifugal  or  motor  projection 
fibers  are  the  following,  namely,  the  intermediate  tract,  the  fronto- 
pontal  tract,  the  pyramidal  tract  and  the  temporo-pontal  tract. 

The  intermediate  tract  {stratum  intermedium  pedunculi,  Figs. 
70,  69  and  87)  extends  from  the  corpus  striatum  through  the  in- 
ferior lamina  of  the  capsule  and  the  deep  part  of  the  basis  pedun- 
culi to  the  motor  cerebral  nuclei  and  to  the  nucleus  pontis,  though 
it  is  probably  relayed  in  the  substantia  nigra.  From  the  nucleus 
pontis  axones  run  by  way  of  the  brachium  pontis  to  the  cortex 
of  the  opposite  hemisphere  of  the  cerebellum.  The  intermediate 
tract  thus  forms  a  segment  of  an  indirect  (through  the  cerebellum) 
efferent,  or  motor  path. 

The  fronto-pontal  tract  {tractus  cerehro-cortico- pontalis  jront- 
alis.  Figs,  70,  71,  69  and  87)  rises  from  the  cortex  of  the  frontal 
lobe  anterior  to  the  precentral  sulci.  It  tranverses  the  centrum 
semiovale,  corona  radiata,  frontal  part  of  the  internal  capsule 
and  medial  one-fifth  of  the  basis  pedunculi  to  the  ventral  area 
of  the  pons,  where  it  terminates  in  the  nucleus  pontis  (chiefly) 
and  in  the  nuclei  of  motor  cerebral  nerves  (Flechsig).  It  is 
probably  relayed  in  the  thalamus  (Beevor  and  Horsley). 

According  to  Dejerine,  the  temporo-pontal  tract  {tractus  cere- 
hro-cortico-pontalis  temporalis,  Figs.  70,  71,  69  and  87)  extends 
from  the  temporal  lobe  through  the  inferior  lamina  (and  posterior 
part  of  the  superior  lamina)  of  the  internal  capsule  and  lateral 
one-fifth  of  the  basis  pedunculi  to  the  substantia  nigra  and  the 


226 


THE    CEREBRUM. 


nucleus  pontis;  but  according  to  Spitzka  some  of  its  fibers  end  in 
the  nuclei  of  motor  cerebral  nerves.  Thus  it  should  be  noted 
that,  with  the  exception  of  those  fibers  to  motor  nuclei  of  the 
cerebral  nerves,  each  of  the  three  tracts  above  mentioned,  viz., 
the  intermediate,  fronto-pontal  and  temporo-pontal,  constitutes 
a  segment  of  an  indirect  efferent  path  which  is  interrupted  in  the 
nucleus  pontis  and  then  continued  by  the  axones  of  that  nucleus 
through  the  brachium  pontis  of  the  cerebellum.  It  is  probable, 
though  not  surely  established,  that  the  fronto-pontal  and  temporo- 


?aV-S^*^      Lentifjrm 


HacLcixi, 


T<?mp  f-'Tr  - 


Fig.  70. — Horizontal  and  sagittal  section  through  internal  capsule,  much  enlarged. 

(Original.) 

Blue,  Common  sensory  tracts:  Fr.  St.,  Frontal  stalk;  Par.  Stalk,  Parietal  stalk;  Ven- 
tral stalk.  Red,  Motor  tracts:  Fr. -P.  Tract,  Fronto-pontal  tract;  Pyr.  Tract,  Pyramidal 
tract;  Temp.-P.  Tr.,  Temporo-pontal  tract;  Interm.  Tract,  Intermediate  tract.  Purple, 
special  sense  tracts:  Opt.  R.,  Occipito-thalamic  radiation;  Acust.  R.,  Temporo-thalamic 
radiation. 

pontal  tracts  are  relayed  in  the  corpus  striatum  or  thalamus,  as 
they  have  been  found  undegenerated  in  the  base  of  the  peduncle 
when  their  cortical  origins  were  destroyed  by  extensive  lesions. 
The  pyramidal  tract  {tractus  cerehro- spinalis  pyramidalis) 
(Figs.  70  and  71)  rises  in  the  anterior  central  gyrus  and  the  pre- 
central  part  of  the  paracentral  lobule.  It  is  composed  of  axones 
from  the  giant  pyramids  and  large  polymorphous  cells  of  that 
region.  Descending  through  the  corona  radiata,  genu  and 
anterior  two-thirds  of  the  occipital  part  of  the  internal  capsule, 
the  pyramidal  tract  comprises  the  middle  three-fifths  of  the  basis 
pedunculi,  enters  into  the  anterior  longitudinal  fibers  of  the  pons. 


PROJECTION    FIBERS.  227 

forms  the  pyramid  of  the  medulla  and  the  anterior  and  lateral 
pyramidal  tracts  of  the  spinal  cord  (Figs.  71,  69,  87,  93  and  102). 
The  fibers  of  the  pyramidal  tract,  with  a  few  exceptions,  cross 
over  to  the  opposite  side;  they  end  in  connection  with  the  motor 
nuclei  of  cerebral  and  spinal  nerves.  Fibers  enter  the  nucleus  of 
the  trochlear  (or  fourth)  nerve  chiefly  on  the  same  side,  and  a 
few  descend  to  the  motor  nuclei  of  other  cerebral  ner\'es  and  to 
the  gray  matter  in  the  spinal  cord  without  decussation;  all  other 
pyramidal  fibers  terminate  on  the  side  opposite  to  their  origin. 
The  fibers  from  the  lower  one-fourth  of  the  anterior  central  gyrus, 
which  go  to  the  motor  nuclei  of  the  cerebral  nerves,  to  a  large  extent 


Fig.  71. — Diagram  of  internal  capsule  in  colors.     (Original.) 
Red,  motor;  blue,  common  sensory;  purple,  special  sensory. 

leave  the  pyramidal  tract  high  up  in  the  peduncle  and  run  for 
some  distance  through  the  medial  portion  of  the  fillet;  they  consti- 
tute Bechterew's  accessory  lemniscus.  This  accessory  fillet  has 
been  recently  traced  by  Flechsig. 

Head  and  Neck  Fibers  (Figs.  70,  105  and  io6). — ^Those  fibers 
of  the  pyramidal  tract  which  end  in  the  nuclei  of  the  cerebral 
and  the  upper  four  cervical  nerves  rise  in  the  lower  segment  of  the 
motor  area,  including  that  part  of  the  anterior  central  gyrus  below 
the  genu  inferius  of  the  central  sulcus.  They  run  through  the 
genu  of  the  internal  capsule  to  the  peduncle  and,  then,  both  through 


228  THE    CEREBRUM. 

the  accessory  fillet  and  the  inner  portion  of  the  middle  three- 
fifths  of  the  basis  pedunculi.  Upper  Extremity  Fibers  (Figs.  70 
and  105).— The  fibers  of  the  pyramidal  tract  that  end  in ,  the 
cervical  part  of  the  spinal  cord,  and  through  it  innervate  the 
muscles  of  the  upper  extremity,  take  their  origin  from  that  part 
of  the  anterior  central  gyrus  adjacent  to  the  foot  of  the  middle 
frontal  gyrus:  their  origin  lies  between  meridians  which  intersect 
the  central  sulcus  at  the  genu  inferius  and  the  genu  superius,  re- 
spectively. These  fibers  run  through  the  pars  occipitalis  of  the 
internal  capsule  just  behind  the  genu,  and  through  the  basis 
pedunculi  immediately  lateral  to  the  head  and  neck  fibers.  Those 
fibers  which  innervate  the  muscles  of  the  thumb,  fingers  and  hand, 
rise  lowest  down  in  the  arm  area  of  the  cortex  and  occupy  the 
posterior  part  of  the  arm  bundle  in  the  internal  capsule  and  the 
lateral  part  of  it  in  the  peduncle.  The  fibers  which  control  the 
shoulder  muscles  rise  in  the  upper  part  of  the  cortical  area  and 
form  the  anterior  and  medial  part  of  the  arm  bundle  in  the  cap- 
sula  interna  and  basis  pedunculi,  respectively;  while  the  wrist, 
forearm,  elbow  and  arm  are  innervated  by  means  of  fibers  which 
are  intermediate  in  both  origin  and  course.  Trunk  Fibers. — 
The  trunk  fibers  of  the  pyramidal  tract  rise  in  that  projection  of 
the  anterior  central  gyrus  which  is  situated  just  above  the  genu 
superius  of  the  central  sulcus.  In  the  internal  capsule,  the  trunk 
fibers  run  just  behind  those  to  the  fingers  and  just  lateral  to  them 
in  the  basis  pedunculi.  Lower  Extremity  Fibers  (Figs.  70  and  105). 
— ^A  large  number  of  the  pyramidal  fibers  terminate  in  the  lumbar 
enlargement  of  the  spinal  cord  and  carry  impulses  to  the  nerves 
of  the  lower  extremity.  They  originate  in  the  upper  fourth  of 
the  anterior  central  gyrus  and  in  the  paracentral  lobule.  The  hip 
fibers  rise  farthest  downward  and  the  toe  fibers  farthest  upward, 
immediately  in  front  of  the  sulcus  centralis.  The  fibers  have 
the  same  relative  position  in  the  internal  capsule;  in  the  base  of 

Description  to  Fig.  72. 

a,  a.  Motor  cells  of  cerebral  cortex,  b,  b.  End-tufts  of  sensory  fibers  in  cortex,  c.  Nu- 
cleus of  funiculus  cuneatus,  showing  end-tufts  of  fibers  from  the  cord.  d.  Nucleus  of  funic- 
ulus gracilis,  containing  end-tufts  of  fibers  from  cord.  e.  Section  of  medulla  at  fillet  de- 
cussation, f.  Section  of  medulla  at  pyramidal  decussation,  g,  g.  Motorial  end-plates. 
h.  Section  of  cervical  cord,  showing  terminations  of  fibers  of  anterior  and  lateral  pyramidal 
tract,  i,  i.  Spinal  ganglia,  j,  k.  Short  sensory  fibers.  1.  Long  sensory  fibers,  m,  m,  m.  Sen- 
sory end-organs,     n.  Section  of  lumbar  cord. 


PROJECTION    FIBERS. 


229 


Fig.  72.— A  diagram  shcnving  motor  and  sensory  paths;  motor  red,  sensory  blue. 
(.-\.ftcr  Gordiiiicr.) 


PROJECTION    FIBERS.  23I 

the  peduncle  the  hip  fibers  are  medial  and  the  toe  fibers  lateral. 
Fibers  which  innervate  the  muscles  of  the  thigh,  leg  and  small 
toes  have  this  same  relative  position  and  order  between  the  hip 
and  great  toe  fibers  both  in  their  cortical  origin  and  in  their  course 
through  the  internal  capsule  and  basis  peduncuH. 

There  are  other  corticijugal  'fibers  in  the  internal  capsule,  viz., 
some  within  the  occipito-thalamic  and  temporo-thalamic  radia- 
tions (Figs.  70  and  71)  and  others  running  from  the  special  and 
common  sensory  areas  of  the  cortex;  but  these  fibers  are  prob- 
ably reflex  in  function  and  do  not  properly  belong  to  the  pro- 
jection group. 

Several  bundles  of  descending  fibers  are  found  in  the  tegmentum, 
namely,  the  anterior  longitudinal  bundle,  which  is  reflex  in  func- 
tion, the  rubro-spinal  tract  from  the  red  nucleus,  a  small  part 
of  the  brachium  conjunctivum  of  the  cerebellum,  the  descending 
root  of  the  trigeminal  nerve,  the  olivary  bundle,  and  certain  other 
fibers  in  the  formatio  reticularis.  With  these  exceptions  the 
tegmentum  is  ascending  in  direction  and  sensory  in  function. 

Destruction  by  clot  or  tumor,  or  otherwise,  of  any  of  the  above 
di\dsions  of  the  pyramidal  tract  causes  upper  segment  paralysis 
of  the  particular  muscles  innervated  through  that  tract,  the  muscles 
being  spastic  and  the  reflexes  increased. 

SENSORY  OR  CORTICIPETAL  PROJECTION  FIBERS. 

The  sensory  or  corticipetal  projection  fibers  of  the  tegmentum 
comprise  the  medial,  superior  and  lateral  fillets;  the  spino-thala- 
mic  tract;  the  brachium  conjunctivum  of  the  cerebellum;  a  part 
of  the  medial  longitudinal  bundle;  and  certain  other  ascending 
fibers  of  the  formatio  reticularis.  Excepting  a  small  number 
of  fibers,  all  these  bundles  terminate  in  the  basal  gangha;  but 
the  paths  of  conduction  are  continued  through  the  internal  cap- 
sule. The  medial  fillet  carries  impressions  of  the  tactile  and  the 
muscular  senses;  the  spino-thalamic  tract  conducts  tactile,  pain 
and  temperature  impulses;  while  all  varieties  of  common  sensory 
impulses  are  carried  by  the  brachium  conjunctivum  cerebelli. 
Chiefly  through  these  three  tracts,  common  sensory  impressions 


232  THE    CEREBRUM. 

arrive  in  the  lateral  nucleus  of  the  thalamus.  In  the  capsula 
interna  the  corticipetal  projection  fibers  constitute  the  cortical 
'fillet  and  the  optic  and  acustic  (and  gustatory?)  radiations.  The 
former  end  in  the  somassthetic  area  of  the  cerebral  cortex,  the 
latter  in  the  visual,  auditory  and  gustatory  cortex. 

The  olfactory  projection  fibers  are  contained  neither  in  the 
tegmentum  nor  in  the  internal  capsule.  They  proceed  from  the 
olfactory  bulb,  through  the  olfactory  tract  and  its  stri^,  directly 
to  the  cerebral  cortex. 

The  exact  origin  of  the  cortical  fillet  (Figs.  70  and  71)  has 
not  been  entirely  determined,  but  it  is  known  to  rise,  chiefly, 
in  the  lateral  nucleus  of  the  thalamus.  The  ventral  stalk  of  the 
thalamus  (Fig.  70)  runs  through  the  internal  capsule,  in  the  inferior 
lamina.  It  is  relayed  largely  in  the  globus  pallidus.  Its  fibers 
enter  the  medullary  laminae  of  the  nucleus  lentiformis  and  the 
external  capsule;  ultimately  they  terminate  in  the  upper  one- 
third  of  the  posterior  central  gyrus  and  in  the  temporal  and  insular 
lobes  (see  p.  212).  From  the  anterior  end  of  the  thalamus  streams 
a  great  pencil  of  fibers,  called  the  frontal  stalk  (Fig.  70).  It  mingles 
to  a  small  extent  with  the  fibers  of  the  pyramidal  tract,  but  runs 
chiefly  through  Ihe  frontal  part  of  the  internal  capsule.  Its 
termination  is  largely  in  the  corpus  striatum;  some  of  its  fibers 
reach  the  frontal  cortex. 

The  parietal  stalk  issues  from  the  lateral  surface  of  the  thala- 
mus higher  up  than  the  ventral  stalk  and  mingles  with  the  pyram- 
idal fibers  in  the  superior  lamina  of  the  internal  capsule.  Its 
location  is  principally  in  the  posterior  third  of  the  occipital  part 
of  the  capsule  (Figs.  70  and.  71).  It  terminates  in  the  para- 
central lobule  and  the  posterior  central  gyrus.  According  to 
Flechsig  some  fibers  also  end  in  the  upper  extremity  of  the  anteiior 
central,  the  superior  frontal  gyri  and  in  the  underlying  part  of 
the  gyrus  cinguli.  The  parietal  stalk,  if  we  may  apply  this  name 
to  all  the  common  sensory  fibers  in  the  occipital  part  of  the  capsule, 
ultimately  comprises  all  the  corticipetal  fibers  to  the  somaesthetic 
area.  Flechsig  gives  their  origin  and  termination,  in  the  order 
of  their  medullation,  as  follows: 

a.  The  alpha  bundle,  a  small  one,  runs  from  the  globus  pal- 


PROJF.CTION    FIBERS.  233 

lidus  to  the  upper  third  of  the  central  gyri,  chiefly  to  the  anterior 
central.     Origin  is  in  doubt. 

iS.  A  large  bundle  from  the  posterior  inferior  part  of  the  lateral 
nucleus  to  the  upper  third  of  the  central  gyri,  chiefly  to  posterior 
central  gyrus  and  adjacent  part  of  the  paracentral  lobule. 

7.  The  gamma  bundle  is  large.  It  runs  from  the  globus 
pallidus  to  same  area  as  beta  bundle.     Origin  is  in  doubt. 

s.  Runs  from  the  lateral  nucleus  of  thalamus  (from  the  central 
of  Luys  and  the  arcuate  nuclei)  to  the  middle  third  of  the  central 
gyri,  principally  to  the  posterior  central. 

e.  A  bundle  from  the  antero-inferior  part  of  the  lateral  nucleus 
to  the  lower  third  of  the  posterior  central  gyrus. 

f.  The  zeta  bundle  is  last  to  be  medullated.  It  rises  in  the 
superior  part  of  the  lateral  nucleus  and  terminates  in  the  foot 
(posterior  end)  of  the  superior  frontal  gyrus  and  in  that 
part  of  the  gyrus  cinguli  which  underlies  the  foot  of  the  first 
frontal. 

The  cortical  fiUel  conveys  common  sensory  impulses  to  the 
somaesthetic  area  of  the  cerebral  cortex.  If  the  cortical  fillet  be 
severed,  all  common  sensory  impulses  to  that  hemisphere  are 
interrupted;  and  complete  loss  of  common  sensation  on  the  oppo- 
site side  of  the  body  and  hemiataxia  result. 

Just  where  the  fibers  conducting  taste  impulses  are  located 
in  the  tegmentum  is  unkno^^'n  Auditory  impulses  run  through 
the  lateral  fillet  and  the  brachium  inferius  to  the  medial  geniculate 
body;  while  optic  impulses  run  directly  to  the  lateral  geniculate 
body  and  the  pulvinar  without  passing  through  the  mid-brain 
at  all.  Within  the  internal  capsule  the  gustatory  tract  cannot 
at  present  be  located;  but  the  acustic  and  visual  paths  are  well 
known. 

The  acustic,  or  temporo-tJialamic  radiation  (Figs.  70  and  54) 
continues  the  auditory  path  from  the  medial  geniculate  body 
through  the  retrolentiform  part  of  the  internal  capsule,  to  the 
transverse  temporal  gyri  and  the  third  and  fourth  fifths  of  the 
superior  temporal  gyrus  (Barker).  Interruption  of  these  fibers 
produces  deafness  in  the  opposite  ear,  which  is  not  complete 
because  the  acustic  patli  is  not  wholly  crossed.     There  are  some 


234  THE    CEREBRUM. 

corticifugal  fibers  in  the  temporp-thalamic   radiation;  they  are 
probably  reflex  in  function. 

The  optic,  or  occipito-thalamic  radiation  (Figs.  70,  38,  45  and 
55)  rises  in  the  lateral  geniculate  body  and  in  the  pulvinar  of  the 
thalamus.  It  continues  the  visual  conduction  path  through  the 
retrolentiform  region  of  the  internal  capsule  to  the  cortex  of  the 
lingual  and  cuneate  gyri.  Half -blindness  in  the  same  side  of 
both  retinee  results  from  section  of  the  optic  radiation.  The 
corticifugal  fibers  in  the  occipito-thalamic  radiation  are  believed 
by  Campbell  to  be  axones  of  the  solitary  giant  cells  (Meynert's) 
in  the  occipital  cortex.  They  run  through  the  lateral  geniculate 
body  and  brachium  superius  to  the  superior  colliculus  of  the 
corpora  quadrigemina,  where  they  end  in  contact  with  the  neu- 
rones of  the  anterior  longitudinal  bundle.  Their  function  is 
reflex. 

II.     COMMISSURAL  FIBERS. 

They  connect  opposite  sides  of  the  cerebrum  and,  like  the 
projection  fibers,  are  continuous  with  the  radiations  of  Mey- 
nert.  They  are  contained  chiefly  in  the  corpus  callosum,  the 
anterior  commissure,  and  the  commissura  hippocampi;  but  are 
also  found  in  the  posterior  commissure,  commissura  hebenularum, 
inferior  (Gudden's)  and  superior  (Meynert's)  commissures. 

The  corpus  callosum,  as  already  described,  is  the  great  link 
between  the  cerebral  hemispheres  (Figs.  34,  27  and  73).  Its 
fibers  connect  both  similar  and  dissimilar  parts  of  the  cortices; 
within  the  hemisphere,  they  form  a  prominent  radiation,  called 
the  radiatio  corporis  callosi.  The  corpus  callosum  is  made  up 
almost  wholly  of  cortical  axones,  a  few  of  them  being  projection 
fibers;  of  a  small  number  of  afferent  projection  fibers,  and  of 
collaterals  from  the  association  and  projection  fibers.  All  callosal 
fibers,  except  the  few  efferent  projection  fibers,  end  on  the  opposite 
side  in  arborizations  within  the  cortex.  It  is  the  corpus  callosum, 
chiefly,  that  makes  it  possible  for  the  two  hemispheres  of  the 
cerebrum  to  act  together  as  one  organ.  Philogenetically,  it  is 
of  recent  development,  since  it  is  not  found  below  mammals. 

The  anterior  commissure   (Figs.  73,  40  and  30)  joins  the 


COMMISSURAL    FIBERS. 


235 


opposite  temporal  and  occipital  lobes  together  {pars  occipito- 
temporalis),  the  limbic  lobes  with  the  contra-lateral  olfactory- 
tracts,  and  the  olfactory  tracts  with  each  other  {pars  oljactoria). 
It  is  supplementary  to  the  corpus  callosum  and  associates  regions 
not  joined  by  the  great  commissure,  especially  the  cortex  of  the 
tentorial   areas   of  the   cerebral  hemispheres.     In  size  it   varies 


F%-  73- — Transverse  section  of  cerebrum,  cutting  corpus  callosum,  anterior 
commissure  and  optic  chiasma.  Viewed  from  front.  Commissural  fibers. 
{Morris's  Anatomy  after  Toldi.) 

a.  Caudate  nucleus  (head),  b.  Internal  capsule  (frontal  portion).  Lentiform  nucleus: 
c.  Putamen,  d  Globus  pallidus.  e.  Medullary  lamina,  f.  External  capsule,  g.  Claustrum. 
h.  Vena  terminalis.  i.  Interventricular  foramen  (Monroi).  j.  Anterior  perforated  sub- 
stance, k.  Uncus.  1.  Anterior  commissure,  m.  Longitudinal  fissure,  n.  Corpus  callosum. 
o.  Anterior  horn  of  lateral  ventricle,  p.  Chorioid  plexus  of  lateral  ventricle,  q.  Septum 
pellucidum.  r.  Columns  of  fornix,  s.  Lateral  fissure  (Sylvii).  t.  Gyri  of  insula,  u.  Optic 
recess,     v.  Optic  tract,     w.  Optic  chiasma.    x.  Inferior  commissure  (Guddeni). 


inversely  as  the  corpus  callosum.  Its  importance  diminishes  with 
the  appearance  of  the  corpus  callosum  in  the  lower  mammalia 
and  it  continues  to  decrease  as  the  higher  forms  arc  approached. 
Below  mammals  it  is  said  to  be  the  most  important  connecting 
link  between  the  hemispheres  and  is  philogenetically  very  old. 


236  THE    CEREBRUM. 

The  commissura  hippocampi,  the  lyre  (Fig.  36),  unites  the 
hippocampal  gyrus,  dentate  fascia,  and  the  hippocampus  with 
their  fellows  of  the  opposite  side.  This  is  the  commissure  of 
the  pyraform  lobes,  the  cortical  areas  of  smell. 

III.     ASSOCIATION  FIBERS. 

These  fibers  remain  on  the  same  side  and  connect  parts  of  the 
same  hemisphere.  They  are  situated  ^\ithin  or  beneath  the 
cortex,  the  various  parts  of  which  they  serve  to  unite.  Association 
fibers  become  medullated  and  actively  functional  only  as  mental 
effort  and  education  gradually  develop  them.  So  far  as  the  brain 
is  concerned  education  consists,  ^rst,  in  the  development  of  the 
functional  centers  of  the  brain;  and,  second,  in  the  establishment 
of  lines  of  rapid  communication  between  them. 

The  short  association  fibers  are  the  more  numerous  and  are 
very  important.  They  unite  contiguous  parts  of  the  same  gyrus  and 
associate  together  adjacent  gyri.  They  are  intralobar.  In  direction 
they  comprise  arcuate  and  tangential  fibers ;  and  they  are  intracort- 
ical  and  subcortical,  in  position.  Every  zone  of  the  cerebral  cortex 
contains  association  fibers,  from  the  felt-work  of  Kaes  to  the 
stratum  zonale.  But  they  are  found  chiefly  (i)  in  the  radiary 
zone  and  adjacent  part  of  the  supraradiary  zone,  along  the  line 
of  Baillarger  (Fig.  60);  and  (2)  in  the  zonal  layer  (Figs.  58  and 
61).  (i)  Those  sparsely  scattered  large  fibers  whose  location  is 
indicated  by  the  line  of  Baillarger  are  called  Meynert's  association 
fibers.  The  deeper  of  these  fibers  are  continuous  with  the  radia- 
tions of  Meynert  and  probably  do  not  belong  to  the  short  asso- 
ciation fibers,  if  associative  at  all  (they  are  corticipetal  fibers); 
the  more  superficial,  intersect  the  radiations  at  right  angles  and 
are  truly  associative  in  function.  The  associative  fibers  of  Mey- 
nert are  compacted  together  by  pressure  in  the  walls  and  floor 
of  the  sulci.  In  the  crown  of  a  gyrus  they  are  scattered.  Their 
exact  origins  are  not  yet  worked  out;  but  they  are  probably  the 
horizontal  processes  of  cells  in  the  second  to  sixth  layers.  (2) 
The  association  fibers  of  the  plexiform  layer  of  the  cortex,  which 
constitute  the  stratum  zonale  (Fig.  61),  are  quite  short  when 
compared  with  those  of  Meynert;  they  join  together  immediately 


ASSOCIATION    FIBERS.  237 

contiguous  parts  within  circumscribed  areas.  The  richness 
of  the  zonal  layer  of  libers,  as  already  pointed  out  in  describing 
the  plexiform  layer  of  the  cortex,  varies  greatly  in  different  regions, 
being  best  developed  in  the  subiculum.  The  fibers  comprising 
the  zonal  layer  have  four  sources  of  origin:  (a)  The  axones  and 
dendrites  of  the  cells  of  Cajal  in  the  plexiform  layer,  fb)  The 
apical  dendrites  of  the  subjacent  pyramids,     (c)  The  T-branched 


Fig.  74. — Diagram  of  association  fibers  in  the  cerebral  hemisphere. 
{Gordinier  and  Qtiain  after  Meynert.) 

s.  Short  association  fibers,  connecting  adjacent  gyri.  f.l.s.  Fasciculus  longitudinalis  su- 
perior, c.i.  Cingulum.  f.p.  Fasciculus  perpendicularis.  f.l.i.  Fasciculus  longitudinalis  in- 
ferior, f.u.  Fasciculus  uncinatus.  jo.  Fornix,  fi.  Crus  fomicis.  v.d'A.  Thalamo-mammil- 
lary  bundle  of  Vicq  d'Azyr. 

axones  of  Martinotti's  cells,     (d)  The  corticipctal  axones  which 
terminate  in  the  superficial  layer  of  the  cortex. 

The  short  association  fibers  are  almost  injinite  in  their  con- 
nections. They  connect  the  receptive  and  psychic  sensor}-  areas, 
and  their  interruption  on  the  left  side  causes  inability  to  interpret 
the  sensations,  called  mind-blindness,  mind-deafness,  stere- 
agnosis,  etc.  x\gain,  those  short  fibers  also  associate  the  psychic 
with  the  psychic-motor,  and  the  psychic-motor  with  the  emissive- 


238  THE    CEREBRUM. 

motor  centers.  In  this  manner  the  writing  center  is  connected 
with  the  motor  center  for  the  upper  extremity,  and  the  speech 
center  with  the  motor  centers  for  the  hps,  tongue,  etc.:  breaking 
of  the  former  connection  on  the  left  side  destroys  ability  to  write, 
agraphia;  and  aphasia  results,  if  the  latter  connection  is  broken. 
Besides  these  and  many  other  connections  of  associated  centers, 
the  short  fibers  join  together  the  various  parts  of  each  cortical 
area. 

The  long  association  fibers  (Figs.  74  and  75)  are  collected 
into  bundles.  They  rise  from  the  pyramidal,  the  polymorphous 
and  the  fusiform  layers  of  the  cerebral  cortex  (Cajal),  and  are 
axones.  Proceeding  out  of  the  lobe  in  which  they  rise,  being 
interlobar,  they  dip  down  into  the  centrum  semiovale  and  arborize 
about  neurones  in  more  or  less  distant  parts  of  the  cortex.  Among 
the  best  known  are  the  following  bundles: 

(i)  The  cingulum  of  the  gyrus  fomicatus  (Fig.  74)  is  a  bundle 
of  fibers  in  that  gyrus  which  almost  entirely  encircles  the  corpus 
callosum.  It  extends  from  the  anterior  perforated  substance 
through  the  gyrus  cinguli  and  hippocampal  gyrus,  to  the  uncus 
and  temporal  pole.  The  fibers,  which  form  several  systems, 
have  been  divided  into  three  groups  by  Beevor,  namely:  (a)  The 
anterior,  which  joins  the  region  of  the  anterior  perforated  sub- 
stance to  the  fore  part  of  the  frontal  lobe,  (b)  The  horizontal, 
which  unites  the  frontal  lobe  and  the  gyrus  fomicatus.  (c)  The 
posterior  fasciculus,  which  associates  the  lingual  and  fusiform 
gyri  with  the  hippocampal  gyrus  and  the  pole  of  the  temporal 
lobe.  Like  the  two  following  bundles  it  establishes  associations 
for  the  sense  of  smell. 

(2)  The  Fornix  (Fig.  74).^ — ^In  each  lateral  half  of  the  fornix 
is  a  bundle  of  association  fibers  as  well  as  of  projection  and  com- 
missural fibers.  The  projection  fibers  rise  in  the  olfactory  bulb 
and  in  the  region  of  the  olfactory  triangle  and,  running  up  through 
septum  pellucidum  to  the  fornix,  continue  through  it  to  their 
destination  in  the  hippocampus  and  uncus.  The  commissural 
fibers  of  the  fornix  rise  in  the  uncus,  the  fascia  dentata  and  gyrus 
hippocampi  and  run  through  the  alveus  of  the  hippocampus  into 
the  crus  fornicis,  whence  they  cross  through  the  commissura  hip- 


ASSOCIATION    FIBERS. 


239 


pocampi  to  the  opposite  side  -(Fig.  36).  They  terminate  in  the 
dentate  fascia  and  hippocampal  gyrus,  including  the  uncus.  The 
associative  group  of  fibers  in  the  fornix  has  the  same  origin  as  the 
commissural  group.  It  enters  crus  fornicis  and  continues  through 
the  body  of  the  fornix  (corpus  fornicis)  into  the  columna,  where 


Fig.  75. — Fasciculus  occipito-frontalis.     Stria  terminalis  and  fasciculus  uncinatus. 
{Gordinier  after  Dejerine.) 

Cge.  Lat.  geniculate  body.  Cgi.  Med.  geniculate  body.  coa.  Anterior  commissure.  Fu. 
Fasciculus  uncinatus.  Gh.  Ganglion  of  the  habenula.  NA.  Amygdaloid  nucleus.  Na.  An- 
terior nucleus  of  thalamus.  NC.  Head  of  caudate  nucleus.  NC'"  Tail  of  caudate  nucleus. 
NC(T).  Body  of  caudate  nucleus.  OF.  Fasciculus  occipito-frontalis.  OF  (Tap).  Part  of  the 
fasciculus  occipito-frontalis  forming  the  tapetum.  pCR.  Foot  of  corona  radiata.  Pul. 
Pulvinar.  sch,  Choriodal  fissure.  Tga.  Columna  of  fornix.  Th  and  ThCVs).  Thalamus. 
tsc(lc).  Stria  terminalis.     tth.  Stria  medullaris  thalami.    II.  Optic  tract. 


it  divides  into  two  unequal  bundles:  The  smaller  is  the  stria 
medullaris  thalami  (pineal  stria)  (Fig.  40),  which  bends  backward 
and  runs  along  the  supero-medial  border  of  the  thalamus  to  the 
nucleus  habenulae ;  in  part  it  decussates  in  the  commissura  habenu- 
larum.  By  the  fasciculus  retroflexus  of  Me}Tiert,  it  is  coimected 
with  the  inter-peduncular  ganglion  of  the  mid-brain.  The  larger 
bundle    continues    as   columna   fornicis    (Fig.    74).     As   already 


240  THE    CEREBRUM. 

indicated,  it  terminates  in  the  medial  nucleus  of  the  corpus  mam- 
millare,  partly  on  the  opposite  side.  Its  termination  is  associated 
first,  with  the  anterior  nucleus  of  the  thalamus  by  the  thalamo- 
mammillary  bundle  (of  Vicq  d'Azyr)  and,  second,  with  the  mid- 
brain and  pons  by  the  pedunculo-mammillary  bundles. 

(3)  The  uncinate  fasciculus  {fasciculus  uncinatus,  Fig.  74)  is 
a  bundle,  with  some  sharply  curved  fibers,  which  arches  over 
the  main  stem  of  the  fissura  cerebri  lateralis,  and  connects  the 
uncus  and  the  anterior  temporal  region  with  the  orbital  gyri  and 
the  pole  of  the  frontal  lobe.  It  is  situated  near  the  basal  surface. 
Its  fibers  spread  out  at  both  ends  in  the  cortex,  and  they  especi- 
ally join  the  medial  and  posterior  orbital  and  the  inferior  frontal 
gyri  with  the  limbic  lobe  (Barker).  Like  the  cingulum  and  for- 
nix, it  is  connected  with  the  rhinencephalon.  Lesion  in  any  one 
of  these  three  bundles  causes  disturbance  of  smell. 

(4)  The  superior  longitudinal  fasciculus  {fasciculus  longit- 
udinalis  superior,  Fig..  74)  is  a  sagittal  bundle  located  beneath 
the  convex  surface  of  the  hemisphere,  just  iabove  the  posterior 
ramus  of  the  lateral  fissure  of  the  cerebrum.  According  to  Cun- 
ningham, it  runs  just  above  and  behind  the  putamen  of  the  lenti- 
form  nucleus,  external  to  the  base  of  the  corona  radiata.  Its 
fibers  diverge  at  the  posterior  end  of  the  lateral  fissure  and  radiate 
into  the  parietal,  occipital  and  temporal  cortex:  some  of  them, 
arching  around  that  fissure,  run  as  far  forward  as  the  temporal 
pole.  The  superior  longitudinal  bundle  joins  the  frontal  cortex 
with  the  parietal,  occipital  and  the  external  temporal.  It  thus 
associates  the  psychic  auditory  and  visual  centers  with  the  motor 
speech  center;  hence  motor  aphasia  is  the  result  of  its  interrup- 
tion. 

(5)  The  inferior  longitudinal  fasciculus  {fasciculus  longit- 
udinalis  inferior,  Fig.  74)  is  about  on  a  level  with  the  lateral 
ventricle.  It  passes  near  the  outer  wall  of  the  inferior  and  posterior 
horns  of  that  ventricle,  being  separated  from  them  by  the  occipito- 
thalamic  radiation  and  the  tapetum.  It  connects  the  temporal 
lobe  to  the  occipital.  In  the  temporal  lobe  its  fibers  cross  at 
right  angles  those  of  the  inferior  lamina  of  the  internal  capsule. 
This  fasciculus  unites  the  auditory  and  visual  psychic  centers,  and 


ASSOCIATION    FIBERS.  241 

thus  associates  the  concepts  of  things  seen  with  those  of  things 
licard.  Breaking  of  this  connection  produces  intercortical  sen- 
sory apJiasia.  So,  an  object  seen  is  recognized,  but  fails  to  sug- 
gest its  name;  and  the  spoken  word  is  heard  and  understood,  but 
does  not  recall  the  visual  picture  of  the  object  or  person  it  repre- 
sents. /According  to  Ferrier  and  Turner  the  inferior  longitudinal 
bundle  is  not  found  in  the  Macaque  monkey,  but  is  present  in  the 
chimpanzee  and  the  orang. 

(6)  The  Fasciculus  Occipilo- frontalis  (Foreli). — ^This  is  a 
large  bundle  of  fibers  formerly  regarded  as  a  part  of  the  corpus 
callosum  (Fig.  75).  It  is  situated  below  the  corpus  callosum 
and,  in  equitorial  sections  of  the  brain,  is  found  in  the  angle  formed 
between  the  callosum  and  the  internal  capsule,  just  external  to 
the  lateral  ventricle.  It  extends  from  the  cortex  of  every  part  of 
the  frontal  lobe  to  the  cortex  of  the  convex  surface  and  lateral 
border  of  the  occipital  lobe.  Posteriorly,  the  fibers  diverge  to 
form  a  fan-like  sheet  in  which  there  is  an  intermingling  of  libers 
from  the  corpus  callosum  (Cunningham);  and  that  sheet  enters 
into  the  external  boundary  of  the  inferior  horn  of  the  lateral 
ventricle  and  into  the  floor,  lateral  wall  and  roof  of  the  posterior 
horn,  hence  the  synonym,  tapetum.  The  tapetum  is  lined  by  the 
ventricular  ependyma  and  is  separated  from  the  inferior  longit- 
udinal bundle  by  the  occipito-thalamic  radiation.  Its  particular 
function  is  unknoArn. 

(7)  The  Perpendicular  Fasciculus  {Fasciculus  Perpendicularis, 
Fig.  74). — ^This  is  a  very  broad  vertical  bundle  located  just  in 
front  of  the  occipital  pole.  It  extends  from  the  inferior  parietal 
and  superior  occipital  gyri,  above,  down  to  the  middle  and  inferior 
temporal,  the  inferior  occipital  and  the  fusiform  gyri.  It  is  often 
classed  with  the  short  association  fibers.     Its  function  is  doubtful. 


16 


CHAPTER  IV. 

THE  RHOMBENCEPHALON. 

SECTION  I.     THE  CEREBELLUM. 

The  rhombencephalon  is  composed  of  the  cerebellum,  the  pons 
and  the  medulla  oblongata  (Figs.  20,  21  and  27).  It  is  the  lozenge- 
shaped  brain.  The  cerebellum  is  the  dorsal  and  largest  portion 
of  it,  and  is  developed  in  the  roof-plate  and  dorsal  zones  of  the 
metencephalon.  Together  with  the  pons  it  forms  the  hind-brain. 
Its  weight  is  about  five  ounces,  slightly  more  than  one-tenth  of 
the  whole  brain.  It  is  situated  in  the  posterior  fossa  of  the  skull, 
under  the  tentorium  cerebelli  and  dorsal  to  the  pons  and  medulla 
oblongata.  Between  it  and  the  last  two  structures  is  enclosed 
the  fourth  ventricle.  The  cerebellum  is  distinguished  from  the 
cerebrum  by  its  stratification.  Its  surface  is  composed  of  gray 
substance,  the  cortex  (substantia  corticalis);  its  interior  is  white 
and  is  called  the  medullary  body  (corpus  medullare,  Figs.  79  and  81). 

Function. — ^The  cerebellum  is  an  important  relay  in  the  in- 
direct motor  and  indirect  sensory  paths.  In  response  to  impulses 
received  from  skin,  muscles,  tendons,  joints  and  viscera,  it  is  also 
believed  to  originate  impulses  which  co-ordinate  muscles  and 
maintain  equihbrium.  Moreover,  according  to  Russel,  each 
cerebellar  hemisphere  exercises  an  important  inhibitory  function, 
through  the  brachia  conjunctiva,  upon  the  opposite  side  of  the 
cerebrum. 

Divisions. — ^The  cerebellum  is  made  up  of  two  lateral  parts, 
the  hemispheres,  and  a  central  part,  uniting  the  hemispheres  to- 
gether, called  the  vermis  cerebelli,  or  worm  (Figs.  76,  77,  and  80). 
In  the  early  embryo  the  cerebellum  is  a  transverse  ridge  in  the 
roof  of  the  fourth  ventricle,  partially  divided  for  a  time  by  a  median 
groove  on  its  ventricular  surface;  and  it  remains  undifferentiated 
into  medial  and  lateral  parts  in  many  lower  animals  (Edinger). 

The  cerebellar  hemispheres  (hemispheria  cerebelli)  measure 

242 


THE    CEREBELLUM. 


243 


two  inches  from  before  backward  and  about  the  same  in  thick- 
ness, antero-medially;  but  they  taper  rapidly  toward  the  lateral 
borders  (Figs.  76  and  77).  They  are  joined  together  by  the  worm, 
or  vermis,  which  forms  the  central  and  most  elevated  part  of  the 
cerebellum. 

The  vermis  cerebelli,  or  worm,  is  a  small  elongated  lobe, 


Fig.  76. — Dorsal  view  of  inter-brain,  mid-brain  and  cerebellum.     Superior  surface 
of  cerebellum.      {Original.) 

a.  Pineal  body.  b.  Colliculus  superior  of  corp.  quad.  c.  Lateral  sulcus,  d.  Colliculus 
inferior  of  corp.  quad.  e.  Culmen  monticuli.  f.  Pars  posterior  of  quadrangular  lobule. 
g.  Superior  semilunar  lobule,  h.  Anterior  tubercle  of  thalamus,  i.  Stria  medullaris  thalami. 
j.  Trigonum'habenulse.  k.  Mid-brain.  1.  Inferior  horn  of  lateral  ventricle,  m.  Pars  an- 
terior of  quadrangular  lobule,  n.  Predeclivil  sulcus,  o.  Postdeclivil  sulcus,  p.  Declive 
monticuli.    q.   Folium  vermis,     r.  Posterior  cerebellar  notch,    s.  Horizontal  sulcus. 


shorter  and  much  thinner  than  the  hemisphere  (Figs.  76  and  80). 
In  animals  lower  than  mammals,  it  is  not  differentiated  from  the 
hemispheres  and  appears  to  be  the  only  part  of  the  cerebellum 
present,  being  very  large  in  birds  and  swimming  reptiles  (Edinger). 
Its  transverse  ridges  give  it  a  worm-like  appearance.  It  unites 
the  upper  half  of  the  medial  aspect  of  the  tw^o  hemispheres,  their 


244  THE    RHOMBENCEPHALON. 

lower  halves  being  separated  by  an  antero-posterior  groove, 
called  the  valley  or  vallecula  cerebelli.  The  upper  surface  of  the 
vermis  is  called  the  superior  worm,  or  vermis  superior;  and  the 
lower  surface,  the  inferior  worm,  or  vermis  inferior.  The  superior 
and  inferior  surfaces  are  separated  from  one  another  at  the  pos- 
terior end  of  the  worm  by  the  great  horizontal  sulcus;  ante- 
riorly, the  medullary  body  of  the  cerebellum  separates  them.  At 
either  end  of  the  worm  is  a  notch  bounded  by  the  vermis  and 
the  hemispheres,  the  anterior  and  posterior  cerebellar  notches. 

The  posterior  cerebellar  notch,  incisura  cerebelli  posterior 
(Fig.  76),  bounded  by  the  posterior  end  of  the  worm  and  the 
postero-medial  border  of  the  hemispheres,  is  occupied  by  the 
falx  cerebelli.  A  prolongation  of  the  medullary  body  of  the 
cerebellum  fills  up  the  incisura  cerebelli  anterior,  or  anterior 
cerebellar  notch,  which  is  situated  between  the  antero-medial 
borders  of  the  hemispheres  in  front  of  the  vermis  cerebelli. 

The  medullary  body  (corpus  medullare)  which  is  the  white 
center  of  the  cerebellum  splits,  in  its  median  part,  into  two  lamina;: 
a  superior,  which  forms  the  superior  medullary  velum  and  three 
pairs  of  connecting  bands  (peduncles),  and  an  inferior,  which  is 
the  inferior  medullary  velum  (Figs.  79  and  78).  Separating  at  an 
acute  angle,  the  two  laminae  form  the  tent  of  the  fourth  ventricle. 

The  inferior  medullary  velum  (velum  medullare  inferius,  Figs. 
79  and  91)  is  the  inferior  lamina  of  the  medullary  body.  It 
is  a  short  plate  of  white  matter,  not  more  than  a  quarter  of  an 
inch  long  and  is  separated  from  the  superior  lamina  by  the  angle, 
called  the  fastigium.  It  ends  in  a  concave  border  from  which  a 
sheet  of  epithelium  continues  down  over  the  fourth  ventricle; 
and  together  they  form  the  inferior  half  of  the  roof  of  that  cavity. 
Laterally,  the  inferior  velum  extends  to  the  flocculus  of  the  hemis- 
phere. Of  the  woim  it  covers  the  nodulus,  antero-superiorly. 
It  bounds,  dorsally,  the  lateral  recesses  of  the  fourth  ventricle. 

In  the  BNA  the  cerebellar  vela  are  called  "  velum  medullare  anterius"  and 
"  V.  m.  posterius;"  but  there  is  no  more  reason  for  those  embryological  terms 
in  this  place  than  there  is  elsewhere  throughout  the  central  nervous  system, 
and  I  have  used  "  superius  "  and  "inferius"  which  properly  indicate  their 
positions  in  adult  anatomy. 


THE    CEREBELLUM. 


245 


The  superior  lamina  of  the  medullary  body  joins  the  cere- 
bellum immediately  to  the  pons.  The  superior  lamina  is  made 
u])  of  three  pairs  of  connecting  bands  (cerebellar  peduncles) 
and  the  superior  medullary  velum.  It  constitutes  all  the  pro- 
longations of  the  corjjus  medullare  of  the  cerebellum,  except 
the  inferior  velum   (Fig.  91). 

The  brachia  conjunctiva  (superior  peduncles,  Figs.  78  and 
86)  converge  as  they  pass  forward  and  upward  to  the  inferior 


o  p  q  r 

Fig.  77. — Anterior  aspect  of  cerebellum.      {Original.) 

a.  Horizontal  sulcus,  b.  Flocculus,  c.  Tonsil,  d.  Superior  medullar^'  velum,  e.  Lob- 
ulus  centralis,  f.  Culmen  monticuli.  g.  Inferior  medullars' velum,  h.  Brachium  conjunc- 
tivum.  i.  Restiform  body.  j.  Brachium  pontis.  k.  Peduncle  of  flocculus.  1.  Division  in 
biventral  lobule,  m.  Lobulus  gracilis,  n.  Lobulus  biventer.  o.  Prepyramidal  sulcus. 
p.  Nodule,    q.  Uvula,    r.  Depression  in  tonsil,     s.  Postnodular  sulcus. 


quadrigeminal  collicuh,  where  they  disappear.  They  are  joined 
to  one  another  by  a  thin  plate  of  white  matter,  the  superior  medul- 
lary velum  {velum  medullare  superius).  With  the  velum,  thev 
form  the  roof  and  lateral  boundaries  of  the  superior  half  of  the 
fourth  ventricle.  They  gradually  bury  themselves  in  the  pons 
as  they  proceed  upward  toward  the  corpora  quadrigemina.  Be- 
neath the  corpora  quadrigemina  and  the  cerebral  aqueduct, 
the  brachia   conjunctiva  cerebelli  decussate,   and  pass  into  the 


246 


THE    RHOMBENCEPHALON. 


hypothalamic  region  of  the  opposite  side.  They  end  chiefly 
in  the  red  nuclei,  which  their  fibers  surround.  Near  the  corpora 
quadrigemina  each  brachium  conjunctivum  is  obhquely  crossed 
by  the  lateral  fillet  in  its  course  to  the  inferior  quadrigeminal 
colliculus. 

The  superior  medullary  velum  {valve  of  Vieussens,  Figs. 
86,  87  and  92),  is  a  trapezoidal  sheet  of  white  substance,  wider 
where  it  fuses  with  the  corpus  medullare  of  the  cerebellum  than 
at  the  mesencephahc  end.  It  forms  the  floor  of  the  groove  between 
the  brachia  conjunctiva  cerebelli  and  the  superior  half  of  the 


Fig.  78. — Dissection  of  rhombencephalon  to  show  brachium  conjunctivum,  brachium 
pontis  and  corpus  restiforme.  {Gordinier,  Sappey  after  Hirschfeld  and  Leveillc.) 

On  left  side  the  cerebellar  brachia  and  restiform  body  have  been  cut  short;  the  right 
hemisphere  is  cut  obliquely  to  show  connection  with  brachium  conjunctivum  and  corpus 
restiforme.  i.  Median  groove  of  fourth  ventricle.  2.  Medullary  striae.  3.  Restiform  body. 
4.  Clava  in  funiculus  gracilis.  5,5.  Brachium  conjunctivum.  6.  Lateral  fillet.  7,7.  Lateral 
sulcus  of  mid-brain.     8.  Corpora  quadrigemina. 

roof  of  the  fourth  ventricle.  Its  lateral  borders  fuse  with  and 
unite  the  brachia  conjunctiva,  hence  their  name.  In  the  median 
hne  its  posterior  surface  presents  a  slight  ridge,  the  jranulum 
veli,  from  either  side  of  which  emerges  the  trochlear  nerve. 

The  corpora  restiformia  (inferior  peduncles  of  the  cerebel- 
lum) issue  from  the  cerebellum  between  the  brachium  conjunc- 
tivum and  the  brachium  pontis  (Figs.  78  and  86).  They  first  run 
forward  to  the  posterior  surface  of  the  pons,  near  the  inferior 
border;  and  then,  bending  downward  and  backward   (a  flexion 


THE    CEREBELLUM. 


247 


of  more  than  90  degrees),  they  converge  in  the  posterior  areas 
of  the  meduUa  toward  the  calamus  scriptorius.  They  help  to 
form  the  floor  and  to  bound  laterally  the  inferior  half  of  the  fourth 
ventricle. 

The  brachia  pontis  (middle  peduncles)  join  the  cerebellum 
to  the  lateral  borders  of  the  pons  (Figs.  78,  85  and  91).  They 
are  continuous  with  the  transverse  fibers  in  the  ventral  area  of 


Fig-  7Q- — Median  section  of  cerebellum,  pons  and  medulla.     (Original.) 

a.  Predeclivil  sulcus,  b.  Arbor  vitse.  c.  Declive  monticuli.  d.  Postdeclivil  sulcus  e. 
Folium  vermis,  f.  Horizontal  sulcus,  g.  Tuber  vermis.  h.  Postpyramidal  sulcus'  i." 
Pyramid,  j.  Prepyramidal  sulcus,  k.  Uvula.  1.  Culmen  monticuli.  m.  Postcentral  sulcus! 
n.  Central  lobule,  o.  Inferior  colliculus  of  corp.  quad.  p.  Cerebral  aqueduct,  q.  Precentrai 
sulcus,  r.  Superior  medullary  velum,  s.  Lingula.  t.  Medial  longitudinal  bundle  u. 
Fastigium.     v.  Inferior  medullary  velum,     w.  Nodule,     x.  Postnodular  sulcus 


the  pons.  The  brachia  pontis  in  the  anterior  cerebellar  notch 
are  placed  external  to  the  brachia  conjunctiva  and  the  restiform 
bodies,  and  are  opposite  the  widest  part  of  the  fourth  ventricle. 
Horizontal  Sulcus  of  Cerebellum  (Figs.  76,  79  and  80).— 
The  cerebellum  has  one  great  sulcus  which  divides  it  into  upper 
and  lower  surface.  The  sulcus  horizonialis  ccrebelli  is  irregularly 
circular  in  shape;  anteriorly  its  lips  are  separated  by  the  prolonga- 
tion of  the  medullary  body  from  which  the  sulcus  runs  backward, 


248  THE    RHOMBENCEPHALON. 

dividing  the  border  of  each  hemisphere  and  the  posterior  end  of 
the  worm.  Rarely  the  two  halves  are  not  continuous  through  the 
posterior  extremity  of  the  worm.  In  the  horizontal  sulcus  the 
remaining  important  sulci  of  the  cerebellum  terminate.  They 
are  nearly  parallel  with  one  another;  hence,  the  cerebellum  is 
laminated,  not  convoluted  like  the  cerebrum.  Though  the 
horizontal  sulcus  is  an  important  landmark  in  the  adult  cerebellum, 
it  does  not  form  a  primary  embryonic  division  of  the  cerebellum 
but  appears  late  in  foetal  life  (Cunningham). 

SUPERIOR  SURFACE  OF  THE  CEREBELLUM. 

The  superior  surface  of  the  cerebellum  (fades  cerebelli  superior) 
is  bounded  by  the  horizontal  sulcus  and  the  superior  lamina  of 
the  medullary  body  (Figs.  76  and  79).  The  posterior  and  larger 
part  of  this  surface  is  covered  by  the  tentorium  cerebelli,  the 
tentorial  area;  the  small  anterior  part  of  it  bounds  the  anterior 
cerebellar  notch.  The  superior  surface  is  divided  into  five  con- 
tinuous lobes  by  four  crescentic  sulci,  called  interlobular  sulci. 

Sulci  of  Upper  Surface. — ^The  interlobular  sulci  {sulci  inter- 
lohulares)  divide  the  worm  and  both  hemispheres  into  lobules; 
and  each  lobe  is' composed  of  a  central  and  two  lateral  lobules. 
These  sulci  are  best  seen  in  a  median  section  of  the  vermis  and 
are  named  in  accordance  with  their  relations  to  the  lobules  in  the 
worm,  viz.: 

(i)  The  precentral  sulcus  {s.  prcEcentralis),  which  is  located 
in  the  anterior  cerebellar  notch  just  above  the  superior  velum 
(Fig.  79).  It  is  between  the  lingula  and  lobulus  centralis,  in  the 
worm;  between  the  vinculum  and  ala,  in  the  hemisphere.  It 
terminates  in  the  horizontal  sulcus.  When  the  vinculum  is 
wanting  the  precentral  sulcus  is  present  only  in  the  vermis. 

(2)  The  postcentral  sulcus  {s.  postcentalis),  in  the  worm, 
separates  the  lobulus  centralis  from  the  culmen;  and,  in  the 
hemisphere,  the  ala  from  the  anterior  part  of  the  quadrangular 
lobule  (Figs.  77  and  79).  The  sulcus  is  situated  at  the  upper 
border  of  the  anterior  cerebellar  notch  and  runs  just  under  the 
anterior  border  of  the  tentorial  surface  of  the  cerebellar  hemis- 


SUPERIOR    SIRFACE    OF    THE    CEREBELLUM. 


249 


])hLTc.      Hotli  central  sulci  Icrminatc  on  the  dorsum  of  the  supe- 
rior mi'(luilar\-  lamina  in  ihe  horizontal  sulcus. 

(3)  Predeclivil  Sulcus.  iS.  prccdecUvis,  s.  primarius)  (Figs. 
76  and  79). — Behind  the  culmen  and  anterior  jjart  of  the  quad- 
rangular lobule,  a  half  inch  from  the  anterior  border  of  the  ten- 
torial surface,  there  is  the  predeclivil  sulcus.  It  bounds  the 
declive  and  posterior  part  of  the  quadrangular  lobule  in  front. 
It  ends  at  the  jimction  of  the  anterior  and  middle  thirds  of  the 
antero-lateral  border  of  the  hemisphere  in  the  horizontal  sulcus. 
Embryologically  it  is  second  to  appear;  it  is  the  deepest  sulcus 
of  the  cerebellum,  hence  the  name,  sulcus  primarius,  given  it 
by  Kuithan.  Its  development  begins  near  the  end  of  the  third 
month  in  utero  (Cunningham). 

(4)  The  postdeclivil  sulcus  (s.  postdecUvis)  (Figs.  76  and 
79)  is  located  in  the  posterior  cerebellar  notch,  from  which  it 
curves  outward  and  forward  in  the  superior  surface  of  the  hemis- 
pheres. It  separates  the  declivil  lobe  from  the  foHum  vermis, 
in  the  worm,  and  from  the  superior  semilunar  lobules  in  the 
hemispheres.  It  ends  in  the  horizontal  sulcus  at  the  junction  of 
the  posterior  and  middle  thirds  of  the  antero-lateral  border. 
Being  behind  the  crescentic  gyri  of  the  quadrangular  lobule, 
this  sulcus  may  be  called  the  sulcus  postlunatus.  It  appears  a 
month  later  than  the  predeclivil  sulcus. 

Sulci  and  lobules  of  the  upper  surface  of  the  cerebellum  from 
before  backward: 


Hemisphere. 

Vinculum 


Worm. 


Lingula 
Precentral  sulcus 
Ala  Lobulus  Centralis 

Postcentral  sulcus 
Lobulus  quadrangularis,       Culmen  ^lonticuli 
pars  anterior. 

Predeclivil  sulcus 
Lobulus  quadrangularis,      Declive  ^Monticuli 
pars  posterior 

Postdeclivil  sulcus 
Semilunaris  superior  Folium  Vermis 

Horizontal  sulcus 


Hemisphere. 

Vinculum 

Ala 

Lobulus  quadrangularis. 
pars  anterior. 

Lobulus  quadrangularis, 
pars  posterior 

Semilunaris  superior 


250  THE    RHOMBENCEPHALON. 

Lobes  of  Superior  Surface  (Figs.  76,  77  and  79). — ^The  lobes 
of  the  superior  surface  of  the  cerebellum  should  be  studied  first 
in  a  median  section,  where  the  branches  of  the  medullary  body 
(lamincE  medullares)  will  guide  the  student  and  where  the  sulci 
are  most  easily  identified.  These  lobes  include  the  divisions 
of  the  worm  and  of  the  hemispheres,  and  are  five  in  number. 

Lingula  and  Vincula,  Lobus  Lingulae. — ^The  lingula  is  a 
very  small  lobule  of  the  vermis  entirely  concealed  in  the  anterior 
cerebellar  notch  by  the  overhanging  central  lobule.  It  is  a  tongue- 
shaped  group  of  four  or  five  rudimentary  transverse  gyri.  It 
rests  upon  the  superior  medullary  velum,  vdth  which  its  white 
center  is  continuous.  Laterally,  the  lingula  tapers  off  and  is 
sometimes  represented  in  the  hemisphere  by  a  very  thin  gyrus 
called  the  vinculum  lingulee.  The  vinculum  is  bounded  by  the 
brachium  conjunctivum  cerebelli  in  front,  and  by  the  precentral 
sulcus  behind.  The  precentral  sulcus  separates  the  lobe  of  the 
lingula  from  the  central  lobe. 

Central  Lobule  and  Alae,  Lobus  Centralis  (Figs.  77  and 
79). — ^The  lobulus  centralis  is  situated  between  the  precentral  and 
postcentral  sulci,  in  the  anterior  cerebellar  notch.  It  covers  the 
lingula  and  in  turn  is  overhung  by  the  culmen.  Four  or  five 
small  transverse  gyri  make  it  up.  On  sagittal  section,  it  is  seen 
to  form  a  single  branch  of  the  corpus  medullar e  (arbor  vitae). 
The  gyri  of  the  central  lobule,  continuing  along  the  anterior  cere- 
bellar notch  into  either  hemisphere,  form  a  triangular  or  wing- 
like lobule,  the  ala  (ala  lobuli  centrahs). 

Culmen  and  Anterior  Part  of  Quadrangular  Lobules, 
Lobus  Culminis  (Figs.  76  and  79). — In  the  culmen  monticuh  the 
surface  of  the  cerebellum  reaches  its  highest  elevation.  It  is  a 
large  lobule  and  occupies  half  of  the  tentorial  surface  of  the  worm. 
It  is  made  up  of  three  or  four  prominent  gyri,  which  extend 
laterally  into  the  hemispheres;  and,  in  each,  forms  the  anterior 
part  of  the  quadrangular  lobule.  The  pars  anterior  lobuli  quad- 
rangularis  occupies  about  one-third  of  the  tentorial  surface  of 
the  hemisphere.  The  predeclivil  sulcus  separates  the  culmen 
and  the  pars  anterior  of  either  side  (the  lobe  of  the  culmen)  from 
the  declivil  lobe. 


INFERIOR    SURFACE    OF    THE    CEREBELLUM.  251 

Declive  and  Posterior  Parts  of  Quadrangular  Lobules,  Lo- 
bus  Declivis  (Figs.  76  and  79). — ^Thc  declive  monticuli  forms  the 
posterior  slope,  as  the  culmen  forms  the  summit,  of  the  monticulus 
cerebelli.  The  declive  has  about  half  the  extent  of  the  culmen. 
Its  gyri  are  continued  into  either  hemisphere,  where  they  form 
a  large  crcsccntic  lobule,  the  pars  posterior  lohuli  quadrangular  is. 
The  increased  size  of  the  lobe  in  the  hemisphere  is  due  to  the 
expansion  of  the  secondary  gyri  found  in  the  worm.  The  anterior 
and  posterior  parts  of  the  quadrangular  lobule  constitute  the 
lobulus  quadrangular  is,  which  forms  the  anterior  two-thirds  of 
the  tentorial  surface  of  the  hemisphere.  The  declive  and  its 
hemispheral  extensions  are  inclosed  between  the  predeclivil 
and  postdeclivil  sulci. 

The  folium  vermis  and  superior  semilunar  lobules,  lobus 
folii  vermis  (Figs.  76  and  79),  lies  behind  the  postdecHvil  and 
above  the  horizontal  sulcus.  The  folium  vermis  is  the  terminal 
lobule  in  the  superior  w^orm,  and  occupies  the  posterior  cerebellar 
notch.  It  appears  near  birth  in  the  bottom  of  a  transverse  groove 
common  to  the  postdeclivil  and  horizontal  sulci  (Cunningham). 
Rarely  it  is  absent.  It  contains  a  single  medullary  lamina  beset 
with  rudimentary  gyri,  which  are  largely  developed  in  the  hemis- 
pheres. The  superior  semilunar  lobule  is,  therefore,  very  large 
in  comparison  mth  the  folium  vermis.  It  expands  lateralward 
to  the  postero-lateral  border  of  the  hemisphere,  which  it  forms. 
It  comprises  the  posterior  third  of  the  hemisphere's  tentorial 
surface,  and  forms  one  of  the  remarkable  features  of  the  human 
cerebellum. 

INFERIOR  SURFACE  OF  THE  CEREBELLUM. 

The  inferior  surface  of  the  cerebellum  (fades  cerebelli  inferior) 
is  prominent  laterally  and  depressed  centrally  (as  the  organ  is 
viewed  inverted),  the  hemispheres  being  separated  by  the  antero- 
posterior groove,  called  the  vallecula  cerebelli  (Figs.  77  and  80). 
The  vallecula  (little  valley)  is  occupied  by  the  inferior  worm  and 
is  bounded  on  either  side  by  a  small  cleft,  between  the  worm  and 
the  overhanging  hemisphere,   called   the  sulcus  valleculce.     The 


252 


THE    RHOMBENCEPHALON. 


inferior  cerebellar  surface  is  limited  by  the  horizontal  sulcus 
and  is  separated  from  the  medulla  by  the  transverse  fissure  of  the 
cerebellum.  It  is  more  complex  than  the  superior  surface;  and 
its  sulci  are  more  sharply  curved  forward  as  they  pass  from  the 
worm  into  the  hemispheres. 

Sulci  of  Lower  Surface  (Fig.  80). — ^The  interlobular  sulci 
of  this  surface  are  very  deep.     They  are  three  in  number,  namely: 

(i)  The  postnodular  sulcus  (s.  postnodularis)  (Figs.  77, 
79  and  80)  is  in  the  anterior  end  of  the  worm  between  the  nodule 


Fig.  80. — Inferior  surface  of  cerebellum.     {Original.) 

a.  Pyramid,  b.  Flocculus,  c.  Nodule,  d.  Brachium  pontis.  e.  Restiform  body._  f.  Su- 
perior medullary  velum,  g.  Brachium  conjunctivum.  h.  Quadrangular  lobule,  i.  Post- 
nodular sulcus,  j.  Uvula,  k.  Tuber'  vermis.  1.  Ant.  and  m.  Post.  Slender  lobules,  n.  In- 
ferior semilunar  lobule,  o.  Tonsil,  p.  Biventral  lobule,  q.  Horizontal  sulcus,  r.  Lobulus 
gracilis,  s.  Prepyramidal  sulcus,  t.  Postpyramidal  sulcus,  u.  Post,  cerebellar  notch. 
V.  Sulcus  valleculas. 

and  uvula.  In  the  hemisphere  it  winds  forward  and  outward 
between  the  inferior  medullary  velum  and  the  tonsil,  and  then 
continues  lateralward  between  flocculus  and  biventral  lobule 
to  the  horizontal  sulcus.  It  is  the  first  cerebellar  sulcus  to  be 
developed  (Cunningham). 

(2)  The  prepyramidal  sulcus   {s.  prcepyramidalis)   (Figs.  79 
and   80),  situated  between  the  uvula  and  pyramid,  is  very  con- 


INFERIOR    SURFACE    OF    THE    CEREBELLUM. 


253 


cave  in  the  hemispheres.  It  curves  outward  and  forward  around 
the  tonsil,  separating  it  from  the  biventral  lobule.  It  terminates 
behind  the  flocculus  in  the  postnodular  sulcus. 

(3)  The  postpyramidal  sulcus  (.v.  poslpyraniidalis)  (Figs 
79  and  80),  between  the  ])yramid  and  tuljL'r  \-ermis,  is  near  the 
posterior  end  of  the  worm.  It  forms  an  oblique  groove  in  either 
sulcus  valleculae,  from  which  three  concentric  sulci  extend  into 
the  hemisphere.  The  anterior  of  the  three  (the  pregracile), 
usually  considered  the  postpyramidal  sulcus  in  the  hemisphere, 
separates  the  biventral  lobule  from  the  slender  lobule  (1.  gracilis); 
the  remaining  two  (midgracile  and  postgracile)  subdivide  the 
slender  lobule  into  anterior  and  posterior  slender,  and  separate 
the  lobulus  gracilis  from  the  inferior  semilunar  lobule.  The 
last  is  bounded  behind  by  the  horizontal  sulcus. 

Sulci  and  lobules  0}  the  lower  surface  of  the  cerebellum,  from 
before  backward: 


Hemisphere. 

Flocculus. 

Tonsil. 

Biventral  lobule. 

Slender  lobule  and  infe- 
rior semilunar  lobule. 


Worm. 

Nodule. 

Postnodular  sidciis. 
Uvula. 

Prepyramidal  sidcus. 
Pyramid. 

Postpyramidal  sidcus. 
Tuber  vermis. 
Horizontal  sulcus. 


Hemisphere. 

Flocculus. 

Tonsil. 

Biventral  lobule. 

Slender  lobule  and  infe- 
rior semilunar  lobule. 


Lobes  of  Lower  Surface. — They  are  not  continuous  from  the 
worm  to  the  hemisphere  as  on  the  upper  surface  (Figs.  76  and  80). 
Excepting  in  the  posterior  lobe,  only  a  small  ridge  beneath  the  sul- 
cus valleculas  joins  the  central  and  lateral  lobules  together.  The 
inferior  lobes  are  four  in  number.  Each  is  composed  of  a  central 
and  two  lateral  lobules  as  on  the  upper  surface.  The  lobule  in 
the  worm  gives  its  name  to  the  lobe. 

Nodules  and  Flocculi,  LobusNoduli  (Figs.  79  and  80). — The 
nodule  (nodulus  vermis)  is  a  small  lobule  at  the  anterior  end  of 
the  inferior  worm.  It  is  composed  of  three  or  four  gyri,  which 
project  from  the  middle  of  the  dorsal  surface  of  the  inferior  med- 
ullary  velum.     It    comprises  a  single  branch  of  the  arbor  vita'. 


254  THE    RHOMBENCEPHALON. 

Though  larger  it  is  the  counterpart  of  the  hngula  on  the  superior 
velum.  It  is  bounded  by  the  sulcus  valleculae  on  either  side. 
The  inferior  medullary  velum  extends  laterally  from  the  nodule, 
and  in  part  blends  with  the  brachium  pontis  of  the  cerebellum. 
In  front  of  the  tonsil,  a  layer  of  gray  matter  {pedunculus  flocculi) 
appears  on  the  velum.  That  gray  matter  enlarges  more  exter- 
nally to  a  small  tufted  mass,  called  the  flocculus,  in  which  the  velum 
ends.  Embryologically,  the  flocculus  is  the  oldest  lobule  of  the 
human  cerebellum,  as  is  the  floccular  sulcus  (postnodular  sulcus) 
which  bounds  it,  the  first  one  formed.  The  flocculus  is  very 
small  and  rudimentary  in  man.  It  is  divided  into  an  anterior 
and  a  posterior  part,  the  latter  being  called  the  secondary  floccu- 
lus. The  flocculus  is  separated  from  the  tonsil  and  the  biventral 
lobule  by  the  postnodular  sulcus.  The  whole  hne  of  structures, 
namely,  the  nodule,  velum,  peduncle  and  flocculus,  form  the 
lobe  of  the  nodule. 

Uvula  and  Tonsils,  Lobus  Uvulae  (Figs.  79  and  80).— The 
uvula  (uvula  vermis)  comprises  a  considerable  part  of  the  vermis 
inferior  behind  the  nodule.  It  broadens  backward  and  is  widest 
next  the  pyramid.  Bounded  on  either  side  by  the  sulcus  vall- 
eculas, it  projects  into  the  valley  like  the  uvula  into  the  isthmus 
of  the  fauces.  It  comprises  one  large  branch  of  the  arbor  vitae 
which  bifurcates  near  its  origin  into  two  laminae  and  presents 
at  the  surface  six  or  eight  small  gyri.  A  shght  ridge,  the  fur- 
rowed band,  joins  it  to  the  tonsil  (tonsilla  cerebelh)  in  the  hem- 
isphere. From  the  furrowed  band  the  tonsil  expands  downward 
and  backward,  forming  a  lobule  of  nearly  a  dozen  sagittal  gyri. 
The  tonsil  overhangs  the  side  of  the  uvula  and  conceals  the  fur- 
rowed band,  medially;  and,  behind,  it  conceals  the  connecting 
ridge  between  the  pyramid  and  biventral  lobule.  Its  large  size 
makes  it  a  prominent  feature  of  the  human  cerebellum.  The 
fossa  containing  the  tonsil  is  the  bird's  nest  (nidus  avis).  Be- 
hind the  uvular  lobe,  composed  of  the  above  three  lobules,  is  the 
prepyramidal  sulcus. 

Pyramid  and  Biventral  Lobules,  Lobus  Pyramidis  (Figs. 
79  and  80). — As  seen  from  the  surface,  three  or  four  distinct 
gyri  make  up  the  pyramid  (pyramis  vermis);  in  reality,  it  covers 


INFERIOR    SURFACE    OF    THE    CEREBELLUM. 


::)D 


one  slron;^  lamina  of  the  arbor  vita;,  which  divides  into  two 
near  the  surface.  It  forms  the  most  prominent  lobule  of  the 
inferior  worm.  A  low  connecting  ridge  joins  the  pyramid  to  the 
biventral  lobule  in  the  hemisphere.  The  bivenlral  lobule  (lobu- 
lus  bi\-enter)  is  triangular  in  outline.  Its  base  looks  toward  the 
flocculus  and  is  bounded  by  the  postnodular  and  the  horizontal 
sulcus;  its  apex  is  continuous  with  the  connecting  ridge  joining 


Fig.  8i. — Sagittal  section  of  cerebellum,  cutting  nucleus  dentatus.     {Original.) 

a.  Sup.  semilunar  lobule,  b.  Corpus  medullare.  c.  Post,  part  quadrangular  lobule,  d. 
Nucleus  dentatus.  e.  Ant.  part  of  quadrangular  lobule,  f.  Interior  of  identate  nuc.  g. 
Central  sulci,  h.  Brachium  pontis.  i.  Restiform  body.  j.  Inf.  semilunar  and  slender 
lobules,     k.  Hilus  of  nuc.  dent.     1.  Biventral  lobule. 


it  to  the  pyramid.  The  gyri  composing  it  radiate  from  the  apex 
toward  the  base,  and  are  divided  into  two  groups  by  a  very  deep 
intralobular  sulcus.  Its  lateral  extension  is  a  httle  beyond  the 
flocculus.  The  postpyramidal  sulcus  bounds  it  postero-exter- 
nally,  and  separates  it  from  the  slender  lobule. 

Tuber  Vermis,  Slender  and  Inferior  Semilunar  Lobules, 
Lobus  Tuberis  (Figs.  79  and  80). — ^The  tuber  vermis  forms  the 
posterior  end  of  the  inferior  worm.  It  resembles  the  lobules  of 
the  ^■ermis  superior,  because  some  of  its  half  dozen  tertiary  gvn 


256  THE    RHOMBENCEPHALON. 

are  continued  into  the  hemispheres,  the  sulcus  valleculae  not  cut- 
ting them  off.  A  bifurcated  lamina  of  the  arbor  vitse  enters  into 
the  tuber.  The  horizontal  sulcus  separates  it  from  the  folium 
vermis  of  the  superior  worm.  The  slender  and  inferior  semilunar 
lobules  comprise  the  posterior  two-thirds  of  the  inferior  surface 
of  each  hemisphere,  extending  from  the  biventral  lobule  to  the 
postero-lateral  border.  Twelve  to  fifteen  gyri  compose  the  lob- 
ules. The  gyri  are  divided  into  three  groups  by  the  midgracile 
and  postgracile  sulci;  the  anterior  and  middle  groups  are  named 
the  anterior  slender  and  posterior  slender  lobules,  they  constitute 
the  lobulus  gracilis.  The  posterior  is  the  inferior  semilunar  lobule. 
The  inferior  semilunar  lobule,  only,  is  continuous  with  the  gyri 
of  the  vermis.  The  great  size  of  the  inferior  and  superior  semi- 
lunar lobules  is  the  most  characteristic  feature  of  the  human  cere- 
bellum. 

The  gray  matter  of  the  cerebellum  is  composed  of  cortex 
which  covers  the  cerebellar  laminae  and  of  ganglia  imbedded  in 
the  medullary  body  (Figs.  81  and  84). 

I.  CORTICAL  GRAY  MATTER. 

The  cortex  of  "the  cerebellum  (substantia  corticalis  cerebelli) 
is  made  up  of  two  thick  layers  visible  to  the  naked  eye,  viz,,  (i) 
a  superficial  layer,  and  (2)  a  deep,  granular  layer.  At  the  junc- 
tion of  these  two  layers  is  a  single  row  of  large  pitcher-shaped  cell- 
bodies,  which  are  characteristic  of  the  cerebellar  cortex  and  are 
often  visible  to  the  unaided  eye.  They  are  the  bodies  of  Purk- 
inje's  cells,  and  are  considered  in  the  deep  part  of  the  first  macro- 
scopic layer,  where  they  form  the  stratum  gangliosum.  Under 
the  microscope  three  layers  are  easily  seen,  viz.,  (i)  the  gray  layer 
(stratum  cinereum);  (2)  the  ganglion  cell  layer  (stratum  gan- 
gliosum); and  (3)  the  granular  layer  (stratum  granulosum). 

(i)  Superficial  Layer  (Figs.  82  and  83). — ^Thickest  on  the 
lamincB  and  thinnest  beneath  the  fissures,  this  layer  contains 
small  and  large  stellate  cell-bodies  with  their  processes,  which 
constitute  the  stratum  cinereum  proper;  and  the  large  Purkinje 
cell-bodies  with  their  dendrites  and  recurrent  axones,  together 


CORTICAL    GRAY    MATTER.  257 

with  ni;in\  torlicipctal  fibers.  The  Purkinje  cells  form  the  slratum 
gangliosum. 

Cells.— The  bodies  of  Purkinje's  cells  (Figs.  82  and  83)  are 
located  near  the  deep  surface  of  the  superficial  layer  in  the 
slratum  gangliosum.  They  measure  from  looit  to  135/i  in  their 
longest  axis.  Each  has  one  axone  which,  after  piercing  the  deep 
layer,  becomes  a  fiber  of  the  medullar^'  body.  It  gives  off,  in  the 
deep  layer,  several  recurrent  collaterals,  which  form  contact  rela- 
tions with  other  cells  in  both  layers.  From  the  outer  end  of 
each  cell-body  antler-like  processes,  the  dendrites,  are  given  off; 
they  ramify  toward  the  surface  in  a  wide  plane  at  right  angles  to 
the  free  border  of  the  gyrus.  The  edge  of  the  plane  only  is  seen 
in  a  longitudinal  section  of  the  gyrus  and  the  arborization  is  very 
narrow  and  tall.  The  stellate  cell-bodies,  an  outer  and  inner 
layer,  together  form  the  stratum  cinereum.  They  increase  in  size 
toward  the  Purkinje  cells.  They  have  rich  dendritic  processes 
and  one  axis-cylinder  each.  Their  processes  ramify  through- 
out the  stratum  cinereum  and  stratum  gangliosum.  The  inner 
layer  of  the  stratum  cinereum  contains  the  larger  cells;  they  are 
called  the  "basket  cells."  Their  axis-cylinder  processes  run 
parallel  ^^dth  the  surface  and  at  right  angles  to  the  border  of  the 
gyrus;  they  give  off  vertical  branches,  which  descend  to  Purkinje's 
corpuscles  and  inclose  them  in  a  basket  work  of  filaments.  In 
the  outer  layer  of  the  stratum  cinereum  the  stellate  cell-bodies 
are  smaller  than  in  the  inner  layer.  They  branch  freely  and  ter- 
minate in  claw-like  end-tufts  in  contact  with  other  stellate  cells. 

The  fibers  of  the  superficial  layer  (Figs.  82  and  83)  have 
three  sources:  (a)  The  processes  of  neurones  within  the  layer, 
which  include  the  dendrites  and  axones  of  the  stellate  cells  and 
the  dendritic  planes  and  recurrent  collaterals  of  Purkinje's  cells. 
(b)  The  processes  of  cell-bodies  in  the  deep  layer,  whose  T- 
branched  axones  pierce  the  dendritic  planes  of  Purkinje  in  the 
first  layer;  and,  the  processes  of  the  large  granules  whose  den- 
drites ramify  toward  the  surface,  (c)  The  fibers  of  the  medullary 
projection  rise  or  end  largely  in  the  cellular  layer.  The  axones 
of  Purkinje's  neurones  compose  all  of  the  corticifugal  fibers. 
They  end  in  the  cerebellar  and  vestibular  nuclei  of  the  cat  (Clark 
17 


258 


THE    RHOMBENCEPHALON, 


and  Horsley)  and  probably  have  these  endings  in  the  human 
brain,  with  the  possible  addition  of  the  inferior  olivary  nucleus. 
The  corticipetal  fibers,  which  rise  either  in  other  parts  of  the 
brain  or  in  the  spinal  cord  and  ganglia,  terminate  in  varicose 
fibrils  chiefly  in  the  superficial  layer.  These  fibrils  entwine  about 
the  "primary  and  secondary  stems  of  the  Purkinje  dendrites" 
(Cunningham). 


Fig.  82. — Section  of  cerebellar  gyrus  made  parallel  with  its  free  border. 
Diagrammatic.  (After  Kblliker  from  Cunningham.) 

G  R.  Small  granules  with  claw -shaped  dendrites  and  long  axones  that  run  out  into  the 
gray  layer  and  divide  T-like.  N.  Axone  of  small  granule.  P.  Purkinje  cells  seen  in  profile, 
showing  border  of  dendritic  planes  in  gray  layer. 


(2)  The  deep,  granular  layer  {stratum  granulosum,  Figs. 
82  and  83)  is  of  uniform  thickness.  It  blends  centrally  with  the 
medullary  projection.  It  contains  a  few  superficial  granules 
which  are  comparatively  large  in  size  and  many  small  granules 
in  which  the  nucleus  occupies  nearly  the  whole  cell-body. 

Cells  of  the  Granular  Layer. ^The  granules  are  small,  round, 
or  stellate  cell-bodies,  largest  near  Purkinje's  cells,  closely  packed 
externally,  but  scattered  among  the  projection  fibers  centrally. 


CORTICAL    GRAY    MATTER. 


259 


Each  small  granule  has  three  to  five  short  dendrites,  which  soon 
Ijrcak  up  into  claw-like  tufts  in  contact  with  adjacent  granules, 
and  one  long  axone.  The  axone  runs  out  into  the  superficial 
layer,  branches  T-like,  and,  piercing  the  dendritic  planes  of  Pur- 


f"ig-  83. — Section  across  a  cerebellar  gyrus  at  a  right  angle  to  the  free  border. 
Diagrammatic.     {Gordiiiier  after  Van  Gehiichten.) 

Showing  large  stellate  cells  of  first  layer  with  their  basket-work  endings;  the  cells  of 
i'urkinje,  their  dendntic  planes  in  the  gray  layer  and  their  axones  running  through  the 
granular  layer  to  the  medullary  lamina  of  the  gyrus;  two  large  granules  of  Golgi  type-  the 
small'granules  whose  T-branches  run  parallel  with  the  border  of  the  gyrus;  moss-like  end- 
mgsjof  Cajal,  etc. 

kinjc,  gives  off  collaterals  to  them  until  exhausted  by  multiple 
division.  The  large  granules  are  dendraxones,  the  type  of  Golgi. 
The  axones  form  remarkable  arborizations  toward  the  meduUarv 
projection,  touching  and  associating  many  granules.  The  den- 
drites, branching  freely,  ramify  in  the  superficial  layer. 


26o  THE    RHOMBENCEPHALON. 

Fibers  of  the  Granular  Layer  (Figs.  82  and  83). — ^The  nerve 
fibers  of  the  granular  layer  are  as  follows:  (a)  The  processes  of 
the  granules,  (b)  the  axones  of  Purkinje's  cells  running  down  into 
the  medullary  projection,  together  with  their  recurrent  collaterals, 
and  (c)  corticipetal  fibers,  most  of  which  run  through  the  granu- 
lar layer,  without  branching,  to  end  in  the  first  layer;  the  remainder 
terminate  in  the  deep  layer  in  the  moss-like  appendages  of  Cajal. 

The  functions  of  the  stellate  cells,  the  "basket  cells"  and  the 
granule  cells  are  probably  receptive  and  associative;  they  receive 
impulses  through  the  projection  fibers  and  transfer  those  impul- 
ses to  the  dendrites  or  bodies  of  Purkinje's  cells.  Purkinje's 
cells  originate  impulses  for  the  coordination  of  muscular  action 
(Gordinier),  and  for  the  inhibition  of  nervous  activity  in  the  op- 
posite cerebral  hemisphere  (Russel).  Lesions  in  the  cerebellum 
produce  incoordination,  chorea,  athetosis  and,  rarely,  convulsions. 

The  neuroglia  of  the  cerebellum  is  similar  to  that  in  the  cere- 
brum. The  short-rayed  cells  are  scattered  throughout  the  gray 
substance,  while  the  long-rayed  are  located  near,  or  within,  the 
white  substance.  In  the  region  of  Purkinje's  cells,  near  the  sur- 
face of  the  deep  layer,  are  the  bodies  of  the  arborescent  cells,  whose 
processes  fonn  a  fine  interlacement  about  the  cell-bodies  of  Pur- 
kinje  and  then  extend  in  parallel  lines  out  to  the  surface.  They 
form  a  neuroglia  felt-work  just  beneath  the  pia  mater  (lamina 
basalis). 

II.     GANGLIONAR  GRAY  MATTER. 

The  ganglia  of  the  cerebellum  are  the  nucleus  dentatus,  nucleus 
emboliformis,  nucleus  globosus  and  nucleus  fastigii  (Figs.  81 
and  84).  All  these  nuclei  are  made  up  of  stellate  cell-bodies, 
which  vary  in  size  from  six  to  forty  microns.  They  form  relay 
stations  in  the  paths  going  out  of  the  cerebellum.  In  them  termin- 
ate axones  of  Purkinje's  cells. 

The  nucleus  dentatus  (corpus  dentatum)  is  a  wavy,  sinuous 
pouch  of  yellowish-brown  gray  matter  imbedded  in  the  medul- 
lary body  of  each  hemisphere.  The  nucleus  dentatus  measures 
a  half  inch  in  length  and  a  quarter  of  an  inch  in  width  (Fig.  81). 


GANGLIONAR    GRAY   MATTER. 


261 


It  is  lilk'd  with  while  ilbcrs,  which  issue  from  its  open  anterior 
end,  called  ihe  hilus,  and  form  the  greater  part  of  the  brachium 
conjuncti\-um  cerebelli.  It  also  receives  many  axones  from  Pur- 
kinje's  cells  and,  thus,  forms  a  relay  in  the  common  sensor}' 
])al!i. 

The  small   ganglia  are  just  visible  to  the  naked  eye  under 
favorable  conditions  (Fig.  84).     One  of  these,  a  club-shaped  mass, 


Fig.  84. — Horizontal  section  of  cerebellum  cutting  nuclei  and  brachia  conjunctiva. 
(Morris's  Anatomy  after  Toldt.) 

a.  Interpeduncular  fossa,  b.  Cerebral  peduncle,  c.  Raphe  of  medulla  oblongata,  d.  Me- 
dial longitudinal  fasciculus,  e.  Lateral  lemniscus,  f.  Substantia  ferruginea.  g.  Superior 
medullary  velum,  h.  Lingula  cerebelli.  i.  Nucleus  emboliformis.  j.  Nucleus  fastigii. 
k.  Nucleus  globosus.  1.  Vermis  (superior),  m.  Posterior  cerebellar  notch,  n.  Pons  (varolii). 
o.  Decussation  of  brachium  conjunctivum.  p.  Stratum  nucleare.  q.  Fossa  rhomboidea 
(pars  superior),  r.  Fourth  ventricle,  s.  Brachium  conjunctivum.  t.  Hilus  of  dentate  nu- 
cleus, u.  Core  of  the  dentate  nucleus,  v.  Dentate  nucleus,  w.  Capsule  of  dentate  nucleus. 
X.  Corpus  medullare.     y.  Cortical  substance,     z.  Medullarv  lamina. 


the  cork-like  nucleus  emboli jor mis,  partly  closes  the  hilus  of  the 
dentate  nucleus.  Medial  to  that  is  an  elongated  antero-posterior 
ganglion,  bulbous  behind,  called  the  nucleus  globosus.  The  third 
nucleus  is  in  the  anterior  end  of  the  worm,  just  above  the  fastigium 
of  the  fourth  wntricle.     It  is  called  the  nucleus  of  the  higrhest 


262  THE    RHOMBENCEPHALON. 

point  of  the  roof,  nucleus  jastigii  (Stillingi).  In  the  last  two  the 
stellate  cell-bodies  are  larger  than  in  the  nucleus  emboliformis 
or  dentatus;  but,  otherwise,  they  are  alike  in  structure.  The 
nucleus  fastigii  and  nucleus  globosus  form  a  part  of  the  origin  of 
the  acustico-cerebellar  tract,  which  descends  to  the  nucleus  of 
Deiters  in  the  medulla;  probably  axones  of  Purkinje's  cells  also 
enter  into  the  acustico-cerebellar  tract  in  man,  as  they  do  in  the 
cat  (Clarke  and  Horsley).  Perhaps  the  nucleus  emboliformis 
and  nucleus  dentatus  have  a  less  important  connection  with  the 
same  tract.  The  small  cerebellar  ganglia,  and  especially  the 
nucleus  fastigii  and  nucleus  globosus,  constitute  a  relay  in  the  arc 
of  equilibrium. 

The  White  Substance  of  the  Cerebellum  (Figs.  79  and  81). 
— ^The  corpus  meduUare  contains  all  the  white  matter  of  the  cere- 
bellum. It  is  a  strong  body  measuring  a  third  of  an  inch  in  thick- 
ness vertically  in  the  middle  of  the  hemisphere,  but  in  the  worm 
it  is  a  thin  sheet  and  is  very  slender  as  seen  in  median  section. 
Its  branches  to  the  cerebellar  gyri  are  called  the  medullary  lamince 
{lamina  medullar es).  Viewed  in  a  sagittal  section  of  the  hemis- 
phere, the  medullary  laminae  are  short  and  stubby  branches  of  a 
very  thick  trunk;  but  the  tree-like  appearance  of  the  medullary 
body  and  laminee  in  the  vermis  is  perfect,  hence  the  name,  arhor 
vitce,  which  is  applied  to  them  there.  In  the  anterior  cerebellar 
notch  the  medullary  body  divides  into  a  thick  superior  lamina 
and  a  thin  inferior  lamina  which  are  separated  by  a  transverse 
furrow,  the  bottom  of  which  constitutes  the  peak,  or  fastigium, 
of  the  fourth  ventricle.  The  inferior  lamina  is  the  inferior  med- 
ullary velum,  already  described;  this,  with  the  continuation  of  its 
ependymal  epithelium,  forms  the  roof  of  the  inferior  half  of  the 
fourth  ventricle.  The  superior  lamina  of  the  corpus  medullare 
forms  the  three  pairs  of  connecting  hands  (peduncles)  and  the 
superior  medullary  velum.  Medullated  axones  make  up  the 
entire  corpus  medullare  and  its  divisions.  We  study  these  axones 
in  three  systems  like  those  of  the  cerebrum: 
I.  Projection,  or  peduncular  fibers. 
II.     Commissural  fibers. 

III.    Association  fibers. 


PROJECTION   FIBERS.  263 

I.     PROJECTION  FIBERS. 

All  fibers  that  leave  the  cerebellum,  or  enter  it,  do  so  through 
the  brachia,  the  restiform  bodies  and  the  superior  medullary 
velum,  hence  these  are  composed  of  projection  fibers.  At  a  higher 
level  the  projection  fibers  are  contained  in  the  corpus  medullare. 

Brachium  Conjunctivum  (Figs.  44,  77  and  78).— The  brach- 
ium  conjunctivum  (superior  peduncle)  is  the  iimermost  of  the  three, 
at  its  origin  in  the  anterior  cerebellar  notch;  external  to  it,  in  the 
notch,  are  the  restiform  body  and  the  brachium  pontis;  and,  in 
the  angle  between  the  brachium  conjunctivum  and  the  restiform 
body,  is  the  vestibular  nucleus  of  Bechterew  (the  upper  part  of 
Deiters's  nucleus).  The  brachium  conjunctivum  is  joined  to 
its  fellow  of  the  opposite  side  by  the  superior  medullary  velum 
{velum  medullare  superius).  Two  bundles  of  fibers  run  through- 
out the  brachium  conjunctivum.  They  are  afferent  and  efl'erent. 
First,  the  fibers  to  the  cerebrum,  which  comprise  nearly  the  whole 
brachium,  are  axones  of  cell-bodies  situated  in  the  nucleus  denta- 
tus.  This  group  of  fibers  partially  buries  itself  in  the  dorsal  area 
of  the  pons,  then  penetrates  the  mid-brain  and  decussates  ventral 
to  the  inferior  quadrigeminal  coIHculi.  It  ends  largely  in  the 
opposite  red  nucleus,  but  partly  in  the  thalamus.  It  constitutes 
one  segment  of  the  indirect  sensor}'  path.  In  the  red  nucleus 
this,  path  is  relayed  to  the  thalamus  and  to  the  cortical  fillet,  or 
the  relay  is  directly  into  the  cortical  fillet.  It  is  probable  that  a 
few  fibers  of  this  brachium  terminate  in  the  nuclei  of  the  third 
and  fourth,  and  perhaps  the  sixth  cerebral  nerves.  The  second 
group  of  fibers  rises  in  the  opposite  red  nucleus,  pursues  a  reverse 
course  and  ends  in  the  nucleus  dentatus.  A  few  fibers  from 
Bechterew's  nucleus  are  found  in  the  cerebellar  end  of  the  bra- 
chium conjunctivum  and  the  fila  lateralia  pontis  traverses  the 
same  part  of  it.  Although  the  greater  number  of  these  fibers 
in  the  conjoined  brachia  decussate  in  the  tegmentum,  a  few'  run 
to  the  red  nucleus  and  thalamus  of  the  same  side;  while  the  fila 
lateraha  cross  in  the  pons  from  the  opposite  pontine  nucleus  and 
the  commissural  fibers  between  Bechterew's  vestibular  nuclei 
leave  the  brachium  and  cross  through  the  superior  velum  in  the 
isthmus.     The  superior  medullary  velum  (Fig.  65)  arches  over 


264  THE    RHOMBENCEPHALON. 

the  fourth  ventricle  between  the  brachia  conjunctiva.  It  is 
composed  of  longitudinal  and  transverse  fibers.  One  distinct 
bundle,  derived  from  the  spinal  cord,  passes  through  it  to  the  worm. 
This  is  the  anterior  ascending  cerebello-spinal  tract  (Hoche). 
The  decussating  root-fibers  of  the  fourth  nerve  (trochlear)  course 
transversely  through  it  and  also  the  commissural  fibers  between 
Bechterew's  nuclei. 

Brachium  Pontis  (Middle  Peduncle,  Figs.  44,  78,  81  and  91). — 
The  brachium  pontis  comes  from  the  pons,  of  which  it  forms  the 
anterior  and  middle  transverse  fibers.  It  enters  into  the  med- 
ullary body  of  the  cerebellum  lateral  to  both  the  brachium  con- 
junctivum  and  the  restiform  body.  According  to  Klimoff  fibers 
running  to  the  cerebellum  make  up  the  entire  brachium  pontis. 
These  are  axones  of  the  nucleus  pontis,  chiefly  the  opposite  one. 
Most  of  them  run  to  the  cortex  of  the  cerebellar  hemisphere;  a 
small  number  runs  to  the  vermis  cerebelli.  They  form  a  seg-- 
ment  in  the  indirect  motor  path  contained,  above  the  pons,  in 
the  medial  and  lateral  fifths  and  the  intermediate  bundle  of  the 
basis  peduncuh.  In  the  cerebellar  end  of  the  brachium  pontis 
we  may  include  the  acustico-cerebellar  tract.  The  latter  is  largely 
a  descending  tract  but  may  contain  some  ascending  vestibular 
fibers.  It  rises 'in  the  cerebellar  nuclei,  and  probably  in  the  gan- 
glionar layer  of  the  cortex;  it  terminates  in  the  nucleus  of  Deiters. 
The  principle  origin  of  the  acustico-cerebellar  tract  is  in  the  oppo- 
site nucleus  fastigii  and  nucleus  globosus.  It  forms  a  part  of  the 
descending  limb  of  the  arc  of  equilibrium.  By  far  the  greater 
number  of  fibers  in  the  brachium  pontis,  whether  efferent  or  affer- 
ent, are  crossed  fibers. 

Possibly  there  are  in  the  brachium  pontis  axones  of  Purkinje's  cells  which 
terminate  in  the  nuclei  pontis  on  both  sides  and  in  the  nuclei  of  the  reticular 
formation. 

The  corpus  restiforme  (inferior  peduncle)  (Figs.  44,  78,  81 
and  91)  can  be  traced  both  to  and  from  the  upper  part  of  the 
hemisphere  and  worm.  Inferiorly,  it  is  the  restiform  body  of 
the  medulla  oblongata.  The  bundles  of  component  fibers  are 
very  numerous:  (i)  The  posterior  cerebello-spinal  fasciculus  (direct 
cerebellar  tract),  whose  origin  is  in  the  dorsal  nucleus  of  the  cord 


COMMISSURAL    FIBERS.  265 

and  terminalion  in  the  superior  worm,  forms  its  central  part. 
(2)  The  external  arcuate  fibers  of  the  medulla  (posterior  and 
anterior)  form  its  free  surface.  They  rise  in  the  nucleus  funic- 
uli gracilis  and  nucleus  funiculi  cuneati  and  end  in  the  vermis 
superior,  the  posterior  on  the  same  and  the  anterior  on  the  oppo- 
site side.  (3)  A  bundle  jrom  the  lateral  nucleus  of  the  medulla 
to  the  cerebellar  cortex  on  the  same  side.  (4)  The  internal  arcu- 
ate fibers  to  the  opposite  lower  olive,  the  cerebello-olivary  tract. 
These  constitute  a  large  part  of  the  deep  area  of  the  restiform 
body  and,  with  the  acustico-cerebellar  tract,  make  up  all,  or  the 
greater  part,  of  the  indirect  motor  path  from  the  cerebellum  to 
the  medulla.  According  to  Cunningham  the  cerebello-olivary 
are  ascending  fibers. 

There  are  probably  a  few  axones  of  Purkinje's  cells  that  run 
down  through  the  corpus  restiforme  and  are  continued  without  in- 
terruption into  the  anterior  descending  cerebello-spinal  tract  of  the 
spinal  cord;  but  surely  the  greater  part  of  that  tract  is  relayed  in 
the  medulla  and  pons,  chiefly  in  the  nucleus  of  Deiters  and  in  the 
inferior  olivary  nucleus. (?) 

It  should  be  noticed  that  the  (posterior)  cerebello-spinal  fascic- 
ulus, the  external  arcuate  fibers  and  the  anterior  ascending  cerebello- 
spinal tract,  with  the  tract  from  the  lateral  nucleus,  are  the  in-com- 
ing parts  of  the  indirect  sensor}'  path,  and  that  the  brachium  con- 
junctivum  is  the  out-going  continuation  of  that  path  up  to  the  red 
nucleus  and  thalamus;  and  again,  that  the  brachium  pontis,  the 
acustico-cerebellar  tract  and  the  descending  fibers  of  the  resti- 
form body  constitute  segments  of  the  indirect  motor  path  and 
have  to  do  with  coordination  and  equilibrium. 

II.  COMMISSURAL  FIBERS. 

The  cerebellar  hemispheres  are  joined  by  transverse  fibers, 
of  which  there  are  two  sets,  namely:  One  near  the  anterior 
end  of  the  worm  beneath  the  central  lobe,  and  the  other  at  the 
posterior  end  of  the  worm. 

III.  ASSOCIATION  FIBERS. 

Limited  areas  of  cerebellar  cortex  are  richly  associated  together 
as  pointed  out  in  the  description  of  the  cortical  gray  substance; 


266  THE    RHOMBENCEPHALON. 

but  there  appears  to  be  nothing  analogous  to  the  long  association 
fibers  found  in  the  cerebrum. 

RHOMBENCEPHALON. 
SECTION  11.     THE  PONS  (VAROLH). 

The  pons  and  medulla  form  the  ventral  part  of  the  rhomben- 
cephalon, the  cerebellum  being  its  dorsal  portion.  By  a  trans- 
verse indentation  of  its  roof,  the  posterior  brain-vesicle  is  parti- 
ally divided  into  an  upper  vesicle,  the  metencephalon,  and  a  lower 
vesicle,  the  myelencephalon;  the  latter  is  the  embryonic  medulla, 
the  former  gives  rise  to  the  cerebellum  and  the  pons.  The  pons 
is  developed  from  the  floor  of  the  metencephalon  (Fig.  79).  It 
is  so  named  because  it  forms  the  connecting  link,  or  bridge,  be- 
tween the  mid-brain,  above,  and  the  cerebellum  and  medulla 
oblongata,  below;  between  the  medulla  and  cerebellum,  and  be- 
tween the  two  cerebellar  hemispheres  (Fig.  85). 

In  shape  the  pons  is  roughly  cylindrical.  It  has  a  broad  basal 
or  ventral  part,  the  pars' basilaris  pontis,  and  a  narrower  dorsal 
portion,  the  pars  dor  salts  pontis  (Fig.  87). 

Size. — ^The  pons  is  about  one  inch  long.  It  is  a  little  broader 
than  long,  and  measures  an  inch,  dorso-ventrally. 

Position. — ^It  rests  in  the  anterior  end  of  the  groove  which 
extends  from  the  foramen  magnum  to  the  dorsum  sellse,  and 
lies  between  and  ventral  to  the  hemispheres  of  the  cerebellum. 
Superiorly,  it  joins  the  mid-brain;  and,  below,  it  is  continuous 
with  the  medulla  oblongata. 

Surfaces  of  the  Pons. — ^The  pons  has  four  surfaces,  viz.,  supe- 
rior (attached);  inferior  (attached);  anterior  (free),  and  posterior 
(partially  free);  and  two  borders,  namely,  right  and  left  lateral, 
continuous  with  the  brachium  pontis  of  the  cerebellum. 

The  superior  and  inferior  surfaces  are  made  by  section,  and 
are  directly  continuous  with  mid-brain  above  and  the  medulla 
below. 

Anterior  Surface  (Tuber  annulare).- — ^The  anterior  surface 
of  the  pons  (Fig.  85)  looks  forward  and  slightly  downward  and 
rests  on  the  sphenoid  bone  behind  the  sella  turcica.     It  is  divided 


267 


Fig.  85. — Anterior  aspect  of  mid-brain,  pons  and  medulla.  (After  Morris's  Anatomy.) 

a.  Anterior  perforated  substance,  b.  Corpus  mammillare.  c.  Cerebral  peduncle,  d. 
Ganglion  semilunare  (gasseri).  e.  Oblique  fasciculus,  f.  N.  hypoglossus  (XII).  g.  Pyramid 
h.  Decussation  of  pyramids,  i.  Insula,  j.  Olfactory-  tract,  k.  Hypophysis.  I.  X.  opticu. 
(II).  m.  Optic  tract,  n.  Tuber  cinereum.  o.  N.  oculomotorius  (III),  p.  Lateral  genicu 
late  body.  q.  N.  trochlearis  (IV).  r.  N.  trigeminus  (M.  P.).  s.  N.  trigeminus  (V).  t. 
N.  abducens  (VI).  u.  Brachium  pontis.  v.  N.  facialis  (VII).  w.  N.  intermedius.  x.  N. 
acusticus  (VIII).  y.  N.  glossopharyngeus  (IX).  z.  N.  vagus  (X).  aa.  X.  accessorius  (XI) 
(spinal  accessory),    bb.  Cervical  I.     cc.  Cerv'ica  .11. 


THE    PONS    (varolii).  269 

into  lateral  halves  by  the  sulcus  basilaris,  containing  the  basilar 
artery;  and  is  bounded  laterally  by  a  sagittal  plane  cutting  the 
root  of  the  trigeminal  nerve.  Vertically  the  surface  is  sHghtly 
convex,  and  is  markedly  so  from  side  to  side.  It  shows  trans- 
verse striations,  which  converge  laterally,  due  to  the  fibers  that 
form  it  and  enter  the  brachia  pontis  of  the  cerebellum.  The 
fibers  of  the  anterior  surface  arc  not  exactly  transverse  in  direction. 
Those  at  the  superior  end  of  the  pons  bend  downward  (fasciculus 
obliquus)  and  form  a  rounded  margin,  which  covers  the  lower 
part  of  the  bases  pedunculi  of  the  mid-brain;  at  the  inferior  ex- 
tremity of  the  pons,  the  fibers  are  convex  downward  and  partially 
conceal  the  pyramids  of  the  medulla  oblongata.  The  two  roots 
of  the  lifth  nerve  (trigeminal)  are  attached  to  the  lateral  border 
(Hcnle)  of  this  surface,  a  little  above  the  middle. 

The  posterior  surface  of  the  pons  is  concealed  by  the  cere- 
bellum (Fig.  88).  It  is  free  in  its  middle  part,  where  it  forms  the 
floor  of  the  superior  half  of  the  fourth  ventricle  (Fig.  86).  The 
ventricular  area  of  the  posterior  surface  is  completely  concealed 
by. the  superior  medullary  velum.  If  examined,  it  is  found  to  be 
divided  into  lateral  halves  by  a  median  longitudinal  groove. 
Each  half  presents  in  its  posterior  part  a  rounded  eminence, 
the  colliculus  facialis,  which  flanks  the  median  furrow  and  is  in 
turn  bounded,  laterally,  by  a  linear  valley,  the  sulcus  limitans, 
lying  near  the  brachium  conjunctivum  cerebelli  and  parallel  with 
it.  The  inferior  end  of  the  valley  is  called  the  fovea  superior; 
its  upper  part  has  a  bluish  tint,  due  to  underlying  pigmented 
cells,  and  is  called  the  locus  cceruleus.  Attached  Area. — ^Lateral 
to  this  ventricular  area,  the  posterior  surface  of  the  pons  is  attached 
to  the  restiform  body  and  the  conjoined  arms  of  the  cerebellum. 
The  restiform  bodies  enter  the  surface  near  the  lower  end  of  the 
pons  and  then  bend  downward  into  the  medufla  oblongata;  while 
the  brachia  conjunctiva,  in  their  course  up  to  the  cerebrum, 
partly  imbed  themselves  in  the  lateral  part  of  the  posterior  surface 
and  form  the  walls  of  the  fourth  ventricle.  The  lateral  fillet 
issues  from  this  surface  just  external  to  the  brachium  conjunc- 
tivum. It  runs  obHciuely  across  the  upper  end  of  the  brachium 
to  the  inferior  colHculus  of  the  corpora  quadrigemina,  and  pro- 


270 


THE    RHOMBENCEPHALON. 


duces  a  flat  striated  ridge,  which  may  be  seen  easily  in  a  well 
hardened  specimen. 

Structure  of  the  Pons. — ^The  pons  is  composed  of  transverse 
and  longitudinal  white  fibers  and  of  gray  matter.     The  trans- 


Fig.  86. — Dorsal  surface  of  pons  and  medulla.     (Morris's  Anatomy  modified  from 

Spalteholz.) 

a.  Median  sulcus,  b.  Superior  fovea,  c.  Limiting  sulcus,  d.  Medial  eminence,  e.  Striae 
medullares.  f.  Inferior  fovea,  g.  Nucleus  funiculi  cuneati.  h.  Taenia  of  fourth  ventricle, 
i.  Area  postrema.  j.  Nucleus  funiculi  gracilis  (clava).  k.  Posterior  median  fissure.  1.  Aquee- 
ductus  cerebri,  m.  Nucleus  incertus.  n.  Locus  caeruleus.  o.  Colliculus  facialis  et  nucleus 
abducentis.  p.  Nucleus  N.  cochlearis  (tuberculum  acusticum).  q.  Area  acustica  (nucleus 
vestibularis),  r.  Nucleus  intercalatus.  s.  Trigonum  N.  hypoglossi.  t.  Ala  cinerea.  u.  Fu- 
niculus separans.     v.  Obex. 


verse  fibers  are  found  chiefly  in  the  basilar  portion  of  the  pons; 
the  longitudinal,  in  both  the  basilar  and  the  dorsal  part.  The 
anterior  longitudinal  intersect  the  deep  transverse  fibers  of  the 
pars  basilaris. 


TRANSVERSE   FIBERS    OF    PONS.  271 

TRANSVERSE  FIBERS  OF  PONS. 

The  transverse  libers  form  three  consecutive  layers  in  the  pons, 
viz.,  the  anterior,  the  middle,  and  the  posterior  layer.  They 
he  one  upon  another.  The  two  former  are  situated  in  the  basilar 
area  of  the  pons,  the  latter  in  the  dorsal  area  (Figs.  87  and  88). 

The  superficial  transverse  fibers  are  anterior  in  position 
and  form  a  thin  compact  layer  constituting  the  anterior  surface 
of  the  pons  (Fig.  87).  They  are  not  intersected  by  longitudinal 
fibers;  but,  otherwise,  are  Uke  the  deeper  transverse  fibers  of  the 
pars  basilaris  pontis. 

Deep  Transverse  Fibers  of  Pars  Basilaris.— These  form  a 
thick  lamina  posterior  to  the  superficial  transverse  fibers  and  in 
contact  with  the  superficial  lamina.  They  are  intermingled  ^nth 
longitudinal  fibers  from  the  bases  pedunculi,  viz.,  the  pyramidal, 
fronto-pontal,  temporo-pontal  and  intermediate  tracts  (Figs. 
87  and  88).  In  the  meshes  between  the  intersecting  fibers  is  a 
large  mass  of  gray  matter,  on  either  side,  called  the  nucleus  pontis. 
The  deep  and  superficial  transverse  fibers  of  the  pars  basilaris 
pontis  form  the  brachia  pontis  cerebelH.  Their  origin  is  found 
in  the  opposite  nucleus  pontis  (Khmoff).  They  continue  the 
indirect  motor  path  from  the  termination  of  the  fronto-pontal, 
temporo-pontal  and  intermediate  tracts  in  the  nucleus  pontis 
to  the  cerebellar  cortex  of  the  opposite  side. 

In  connection  with  the  superficial  and  deep  transverse  fibers 
in  the  basilar  part  of  the  pons  there  should  be  mentioned  an 
independent  strand,  the  fila  lateralia  pontis,  which  is  situated 
at  the  upper  border  of  the  pons  and  buried  more  or  less  in  the 
isthmian  furrow  between  the  pons  and  mid-brain.  It  is  called 
by  Henle  the  taenia  pontis.  According  to  Sir  Victor  Horsley,  it 
rises  from  the  nucleus  pontis  just  ventral  to  the  interpeduncular 
gangHon,  and,  ^\^nding  round  the  isthmus,  enters  the  cerebellum 
through  the  bracliium  conjuncti\-um.  Its  destination  is  probably 
the  nucleus  dcnlatus  and  nucleus  fastigii  (Brain, Vol.  29,  No.  113). 

The  transverse  fibers  of  the  pars  dorsalis  pontis  (Fig.  88) 
compose  a  thin  layer  on  the  dorsum  of  the  middle  transverse 
fibers,    separating    them    from    the    formatio    reticularis.     This 


272  THE    RHOMBENCEPHALON. 

transverse  lamina  is  present  only  in  the  inferior  part  of  the  pons. 
It  is  called  the  corpus  irapezoideum. 

The  trapezoid  body  (corpus  trapezoideum)  lies  in  the  dorsal 
area  of  the  pons,  next  the  boundary  between  the  pars  basilaris 
and  the  pars  dorsalis  pontis.  Its  fibers  rise  chiefly  from  the 
nuclei  of  the  cochlear  nerve  and,  after  decussating  in  the  raphe, 
are  continued  up  in  the  lateral  fillet  to  the  inferior  quadrigeminal 
colliculus.  A  few  fibers  join  the  tract  directly  from  the  cochlear 
nerve.  The  nuclei  of  the  trapezoid  body  and  of  the  superior  olive 
form  relays  for  a  number  of  its  fibers.  The  corpus  trapezoideum 
with  the  medullary  striae,  and  the  lateral  fillet,  which  is  the  con- 
tinuation of  both,  form  the  second  stage  in  the  auditory  conduction 
path;  and  the  auditory  impulses  are  continued  (a)  through  the 
brachium  quadrigeminum  inferius  and  (b)  the  temporo-thalamic 
radiation  to  the  temporal  cortex  (Fig.  89). 

LONGITUDINAL  FIBERS  OF  PONS. 

The  longitudinal  fibers  of  the  pons  are  arranged  in  two  distinct 
groups,  viz.,  the  ventral  or  anterior  and  the  dorsal  or  posterior 
(Figs.  87  and  88).  The  groups  are  separated  by  the  trapezoid 
body. 

The  ventral  longitudinal  fibers  are  situated  in  the  pars  bas- 
ilaris pontis  (Figs.  87  and  88).  Four  fasciculi  make  them  up. 
They  are  the  four  motor  tracts  of  the  basis  pedunculi.  The  fronto- 
pontal,  temporo-pontal  and  intermediate  tracts  terminate  in  the 
nucleus  pontis.  The  pyramidal  fibers  run  from  the  middle  three- 
fifths  of  each  basis  pedunculi  down  through  the  middle  trans- 
verse layer  of  the  pons  to  the  pyramids  of  the  medulla  oblon- 
gata. Together  with  the  above  cerebro-pontal  tracts  they  form 
a  thick  bundle  on  either  side  of  the  median  line,  which  presses 
down  the  superficial  transverse  fibers  and  produces  the  sulcus 
basilaris.  The  nucleus  pontis,  one  on  either  side,  is  situated  among 
the  pyramidal  fibers.  The  pyramidal  tracts  diminish  in  size  dur- 
ing their  descent,  because  of  the  fibers  which  leave  them  to  de- 
cussate and  end  in  the  nuclei  of  motor  cerebral  nerves. 

The  Dorsal  Longitudinal  Fibers. — ^These  are  contained  in 


LONGITUDINAL    FIBERS    OF    PONS.  273 

the  pars  dorsalis  poiilis  m  the  formatio  reticularis  (Figs.  87  and  88). 
They  arc  dorsal  to  the  corpus  trapczoidcum,  and  lie  in  the  floor 
of  the  fourth  ventricle,  where  they  are  intermingled  with  the  ven- 
tricular gray  substance.  They  do  not  form  a  compact  layer, 
but  arc  collected  into  a  number  of  distinct  strands,  of  which  the 
larger  are  visible  to  the  naked  eye  in  Weigcrt-Pal  sections.  The 
dorsal  longitudinal  fibers  arc  mingled  with  many  transverse  and 
oblique  fibers;  and,  thus,  there  is  produced  the  netlike  arrange- 
ment suggesting  the  name,  jormatio  reticularis.  The  formatio 
reticularis  of  the  pons  is  continued  down  from  the  tegmentum 
of  the  mid-brain  and  comprises  the  tegmental  region  of  the  pons. 
The  gray  matter  in  the  meshes  of  this  network,  which  is  the 
stratum  nucleare  continued  up  from  the  medulla,  contains  the 
nuclei  of  the  iifth,  sixth  and  seventh  cerebral  nerves  and  a  part 
of  the  nucleus  of  the  eighth  nerve,  and  also  the  nuclei  of  the  for- 
matio reticularis,  viz.,  the  nucleus  centralis  superior,  medius 
and  inferior,  and  the  nucleus  lateralis  medius.  In  the  formatio 
reticularis  are  the  nine  bundles  or  tracts  of  fibers  that  constitute 
the  dorsal  longitudinal  fibers  of  the  pons.  These  tracts  are  as 
follows:  The  anterior  ascending  cerebello-spinal  tract,  the  spino- 
thalamic tract,  the  medial  fillet,  the  lateral  fillet,  the  medial  (pos- 
terior) and  anterior  longitudinal  bundles,  the  rubro-spinal  tract, 
the  olivar)^  fasciculus,  and  the  descending  root  of  the  fifth  cere- 
bral nerve,  besides  unidentified  fibers  of  the  formatio  reticularis 
which  are  probably  both  ascending  and  descending  in  conduc- 
tion. The  anterior  ascending  cerebello-spinal  tract  and  the 
descending  root  of  the  trigeminal  (or  fifth)  nerve  are  the  only 
tracts  not  already  considered  in  our  study  of  the  tegmental  region 
of  the  mid-brain,  page  156. 

(i)  The  medial  fillet  (lemniscus  medialis,  Figs.  87  and  88) 
is  a  large  bundle  of  fibers  that  runs  through  the  pons  next  the 
median  plane.  In  the  lower  part  of  the  pons  it  Hcs  dorsal  to  the 
trapezoid  body,  though  some  of  the  trapezoidal  fibers  pierce  it. 
Its  origin  is  found  on  the  opposite  side  in  the  nucleus  funicuh 
gracilis  and  nucleus  funiculi  cuneati  and  in  the  terminal  nuclei 
of  common  sensory  cerebral  nerves  (Fig.  94).  It  conducts  im- 
pulses of  tlie  tactile  and  muscular  senses.  In  the  mid-brain  it 
18 


274  THE    RHOMBENCEPHALON. 

gives  off  the  superior  fillet  {lemniscus  superior)  which  terminates 
in  the  superior  quadrigeminal  coUiculus.  The  medial  fillet  ends 
in  the  lateral  nucleus  of  the  thalamus  (Fig.  47).  Interruption  of 
the  medial  lemniscus  causes  ataxia  on  the  opposite  side. 

(2)  Lateral  Fillet.  (Lemniscus  lateralis). — ^The  lateral  fillet 
forms  a  link  in  the  special  sense,  auditory  path  (Fig.  89).  As 
stated  on  page  160  it  is  but  the  longitudinal  continuation  of  the 
corpus  trapezoideum  and  the  medullary  striae.  It  takes  form 
near  the  middle  of  the  pons,  where  the  fibers  of  the  trapezoid  body 
bend  upward  to  a  longitudinal  direction;  and  it  runs  just  lateral 
to  the  medial  fillet  (Figs.  86  and  87).  Very  soon  it  becomes  sepa- 
rated from  the  medial  fillet  by  the  brachium  conjunctivum  of  the 
cerebellum.  It  runs  dorso-medially  over  the  conjoined  brachium 
to  the  inferior  colKculus  of  the  corpora  quadrigemina,  where  a 
few  of  its  fibers  end;  but  the  greater  number  are  continued  through 
the  brachium  inferius  to  the  medial  geniculate  body.  The  chief 
origin  of  the  lateral  fillet  is  found  in  the  opposite  cochlear  nuclei, 
though  some  of  its  fibers  rise  in  the  nucleus  of  the  corpus  trapez- 
oideum, the  superior  oUvary  nucleus,  and  the  nucleus  of  the 
lateral  fillet,  which  constitute  partial  relays  in  the  auditory  path. 
It  is  also  true  that  a  few  fibers  enter  the  lateral  fillet  from  the 
cochlear  nuclei  and  nerve  of  the  same  side;  they  are  supposed  to 
decussate  near  or  in  the  quadrigeminal  bodies  and  terminate  in 
the  opposite  inferior  colliculus.  Destruction  of  the  lateral  fillet 
causes  deafness,  almost  complete,  in  the  opposite  ear. 

(3)  The  spino-thalamic  tract  occupies  the  lateral  part  of 
the  formatio  reticularis  where  it  is  intermingled  with  the  anterior 
ascending  cerebello-spinal  tract  (Figs.  87  and  88).  As  already 
stated,  it  rises  in  the  spinal  cord  from  the  basal  gray  substance 
of  the  anterior  columna  and  from  the  terminal  nuclei  of  common 
sensory  cerebral  nerves  in  the  medulla  and  pons.  The  spino- 
thalamic tract  ends  in  the  lateral  nucleus  of  the  thalamus.  It 
conducts  impulses  of  the  tactile,  pain  and  temperature  senses. 

(4)  The  anterior  ascending  cerebello-spinal  tract  has  the 
same  spinal  origin  and  function  as  the  spino-thalamic  tract  and 
the  same  course  up  to  the  isthmus  rhomb encephali  (Figs.  87  and 
88).     There,  it  bends  backward,  medial  to  the  brachium  con- 


LONGITUDINAL    FIBERS    OF    PONS. 


275 


junctivum,  and,  tlirough  the  superior  medullary  velum,  enters 
the  superior  worni  of  the  cerebellum.  It  thus  belongs  to  the  in- 
direct sensory  path  (through  the  cerebellum).  From  the  cerebellar 
cortex  the  path  is  continued  by  the  axones  of  Purkinje's  cells  to 
the  nucleus  dentatus,  whence  the  brachium  conjunctivum.  com- 
pletes it  up  to  the  opposite  red  nucleus  and  thalamus.  The  an- 
terior ascending  cerebello-spinal   and   the   spino-thalamic   tracts 


d    e 


Fig.  87. — Superior  section  of  the  pons.     {Original.) 

a.  Beginning  of  decussation  of  brachium  conjunctivum.  b.  Formatio  reticularis,  c- 
Brachium  conjunctivum.  d.  Medial  longitudinal  bundle,  e.  Fourth  ventricle,  f.  Superior 
medullary  velum,  g.  Descencding  root  of  5th  n.  h.  Spino-thalamic  tract,  i.  Lateral 
fillet,  j.  Medial  fillet,  k.  Long,  fibers  from  basis  pedunculi.  1.  Superficial  transverse  fibers. 
m.  Nucleus  pontis.     n.  Deep  transverse  fibers  of  pjirs  basilaris  pontis. 

arc  the  chief  bundles  of  a  spino- encephalic  system  of  fibers  which 
terminates  very  largely  in  the  cerebellum  and  thalamus,  but  also 
sends  fibers  to  the  nucleus  lateralis  inferior  and  other  reticular 
nuclei,  to  the  substantia  nigra,  to  the  inferior  and  superior  collic- 
uli  of  the  corpora  quadrigemina,  to  the  nucleus  ruber,  the  nu- 
cleus hypothalamicus,  and  the  corpus  striatum.  In  tliis  spino- 
encephalic   system   there    are   two   important   paths — the   direct 


276  THE    RHOMBENCEPHALON. 

path  (No.  3)  and  the  indirect  path  (No.  4) — for  tactile,  pain  and 
temperature  impulses.     It  is  called  Gowers^s  tract. 

(5)  The  medial  (posterior)  longitudinal  bundle  (fasciculus 
longitudinalis  medialis)  (Figs.  87  and  88)  runs  next  the  median 
plane  and  just  under  the  ventricular  gray  matter  in  a  position 
similar  to  the  one  it  occupies  in  the  mid-brain  (Figs.  47  and  48), 
see  page  156.  It  is  in  the  pontine  portion  of  this  bundle  that 
the  fibers  from  the  oculomotor  nucleus  pass  to  the  genu  of  the  fa- 
cial nerve,  ultimately  to  innervate  the  frontalis,  corrugator  and  or- 
bicularis oculi ;  it  is  in  the  pons,  that  fibers  from  the  abducent  nu- 
cleus join  this  bundle,  and  run  upward  through  it  to  the  oculo- 
motor nucleus  of  the  opposite  side  and  make  possible  the  conju- 
gate movements  of  the  eyeballs;  it  is  also  here,  that  fibers,  which 
rise  in  the  hypoglossal  nucleus,  leave  the  longitudinal  bundle  and 
enter  the  facial  nerve  at  the  genu  to  be  distributed  by  way  of 
the  facial  to  the  orbicularis  oris.  As  in  the  mid-brain,  the  longit- 
udinal bundle  includes  the  two  functional  tracts,  the  descending 
strand  and  the  ascending  strand. 

(6)  Anterior  Longitudinal  Bundle. — ^This  ocular-reflex  bundle 
is  continued  from  the  mid-brain  down  through  the  pons  in  nearly 
the  same  relative  position.  Diverging  a  little  from  the  medial 
longitudinal  bundle  as  it  descends  through  the  pons,  it  is  located 
in  the  formatio  reticularis  a  short  distance  ventro-lateral  from  it. 
The  anterior  longitudinal  bundle  can  be  recognized  in  normal 
adult  tissue  only  in  the  dorsal  tegmental  decussation  (Meynerti) 
of  the  mid-brain:  lower  down  it  can  be  distinguished  from  the 
surrounding  tissues  by  degeneration  and  meduUation  but  in  no 
other  way  (Fig.  87).  Having  given  fibers  to  the  oculomotor  and 
trochlear  nuclei  above,  it  sends  fibers  to  the  nucleus  of  the  abdu- 
cent nerve  at  this  level,  and  perhaps  to  other  pontine  nuclei  (see 
Mid-brain,  page  158). 

(7)  Rubro-spinal  Tract. — In  the  mid-brain,  we  have  traced 
this  tract  from  the  red  nucleus,  through  the  ventral  tegmental 
decussation  (Foreh),  to  the  opposite  side,  where  it  mingles  with 
the  lateral  fillet  down  near  the  isthmus  (Figs.  47  and  48).  It 
occupies  the  same  position  in  the  upper  half  of  the  pons ;  it  is  close 
to  the  posterior  surface  of  the  corpus  trapezoideum  in  the  lower 


LONGITUDINAL    FIBERS   OF    PONS. 


'// 


pari  of  tin-  pons  (Fij^s.  87  and  88).  In  the  center  of  ihe  gray 
cresci'nl  of  llie  s])inal  cord  the  rubro-spinal  tract  ends.  Its  func- 
tion is  unknown,  ])erliaps  it  has  to  do  with  locomotion  (Horshy)v 
(8)  The  olivary  bundle  (jasriculus  olivaris)  is  regarded  by 
many  as  an  ascending  tract,  but  the  weight  of  evidence  at  present 
is  in  favor  of  a  descending  course.  Rising  in  the  Icntiform  nucleus 
and  descending  through  the  mid-brain,  it  enters  the  center  of  the 


Nucleus  globosus     i  Colliculus  facialis 


Nuclei  of  sth  nerve 


Nucleus  emboliformis 
Hilus  of  nuc.  dentatus 
Nuc.  of  bechti  •,',',  \  -  y,.  ^: 


Nucleus  fastigii 

Nucleus  of  abducent  n. 


Medial  longitudinal 
bundle 


Tractus  spinalis  N.  trigemini 

Superior  olivary  nucleu 


Nucleus  of  facial  n. 
Formatio  reticularis 


Transverse  fibers  to  brachium  pontis 
Pyramidal  tract 


Trapezoid  body  and  medial  fillet 
Fig.  88. — Inferior  section  of  the  pons  together  with  the  cerebellum.     (Original.) 


reticular  formation  of  the  pons,  hence  the  name,  central  tegmental 
tract  (Fig.  88).  It  runs  dorsal  to  the  medial  fillet  and  the  corpus 
trapezoideum  in  the  lower  part  of  the  pons,'  just  medial  to  the 
superior  olivary  nucleus.     It  terminates  in  the  inferior  olive. 

(9)  The  descending  root  of  the  trigeminal  nerve  (Fig.  87) 
is  crescentic  in  section  and  runs  between  the  ventricular  gray 
substance  and  the  brachium  conjunctivum  of  the  cerebellum  dowD. 
to  the  middle  of  the  pons,  where  it  joins  the  principle  motor  root. 
It  passes  lateral  to  the  motor  nucleus  situated  under  the  locus 


278  THE    RHOMBENCEPHALON. 

caeruleus,  and  runs  between  it  and  the  superior  end  of  the  ter- 
minal or  sensory  nucleus. 

In  the  lowest  part  of  the  pons  there  is  seen  the  spinal  tract  of 
the  fifth  nerve  {tracus  spinalis  nervi  trigemini).  This  is  a  part 
of  its  sensory  root  and  is  composed  of  the  descending  limbs  of 
T-branched  axones  from  the  semilunar  ganglion  (Gasseri).  The 
spinal  tract  of  the  trigeminal  nerve  runs  lateral  to  the  gray  sub- 
stance,, between  the  substantia  gelatinosa  (Rolandi),  on  the  inner 
side,  and  the  vestibular  root  of  the  acustic  nerve  and  the  resti- 
form  body  on  the  outer  side. 

GRAY  MATTER  OF  THE  PONS. 

In  the  pons  gray  matter  is  found  in  two  situations:  (i)  In 
the  interstices  between  the  deep  transverse  fibers  of  the  pars 
basilaris  pontis  and  the  ventral  longitudinal  fibers,  the  nuclei 
pontis;  and  (2)  in  the  formatio  reticularis,  just  under  the  fourth 
ventricle  where  it  forms  the  stratum  nucleare. 

The  nucleus  pontis  is  a  mass  of  gray  matter,  on  either  side 
the  raphe,  containing  the  bodies  of  large  multipolar  nerve  cells 
whose  axones  run  through  the  brachium  pontis  of  the  cerebellum 
to  the  cortex  on  the  opposite  side.  It  extends  vertically  throughout 
the  pons  and  is  continuous  with  the  arcuate  nucleus  of  the  medulla. 
The  nucleus  pontis  receives  the  terminals  of  the  descending  tracts 
which  form  the  inner  and  outer  fifths  of  the  basis  pedunculi  and 
the  intermediate  bundle  of  the  same,  and  thus  connects  these 
tracts  with  the  cerebellum.  It  forms  a  relay  in  the  indirect  motor 
path. 

The  gray  matter  of  the  stratum  nucleare  includes  (i)  the 
olivary  group  of  nuclei,  viz.,  the  superior  oHvary  nucleus,  the 
nucleus  of  the  corpus  trapezoideum,  the  preolivary  nucleus  and 
the  semilunar  nucleus;  (2)  the  nuclei  of  the  formatio  reticularis, 
viz.,  the  nucleus  centralis  superior,  medius  and  inferior,  and  the 
nucleus  lateraHs  medius;  and  (3)  the  nuclei  of  cerebral  nerves — 
the  fifth,  sixth  and  seventh,  and  a  part  of  the  vestibular  nucleus 
of  the  eighth  nerve. 

(i)  Olivary  Group. — ^The  superior  olivary  nucleus  (n.  olivaris 


GRAY  MATTER  OF  THE  PONS.  279 

superior)  is  situated  in  the  lateral  part  of  the  formatio  retic- 
ularis in  the  dorsal  portion  of  the  corpus  trapezoideum  (Fig.  88). 
It  lies  just  ventral  to  the  nucleus  of  the  facial  ner^^e  and  ventro- 
lateral to  the  olivary  bundle  of  fibers.  The  nucleus  contains  small 
bodied  nerve  cells;  and,  in  this  respect,  resembles  the  ohve  of  the 
medulla.  Its  outhne  is  crescentic,  convex  toward  the  median 
line.  In  size  it  is  microscopic.  According  to  Bruce  and  Cun- 
ningham it  is  continuous  mth  the  nucleus  of  the  lateral  fillet. 
The  superior  olive  constitutes  a  subordinate  relay  in  the  auditory 
path,  receiving  fibers  from  the  cochlear  nuclei  of  both  sides  and 
contributing  fibers  to  both  lateral  fillets  (Fig.  89). 

The  superior  olivary  nucleus  gives  off  a  small  strand  of  fibers, 
called  the  olivary  pedicle,  which  runs  dorso-medially,  between  the 
recurrent  and  emergent  parts  of  the  root  of  the  facial  nerve,  to 
the  nucleus  of  the  abducent  nerve;  there  some  of  its  fibers  end, 
the  remainder  join  the  medial  longitudinal  bundle  and  run  to  the 
trochlear  and  oculomotor  nuclei.  The  pedicle  forms  part  of  an 
auditor}^-ocular  reflex  arc. 

A  small  accessory  nucleus,  called  the  nucleus  prceolivaris,  is 
situated  just  a  Httle  ventral  to  the  superior  olivary  nucleus;  and  a 
second  one  embraces  the  convexity  of  the  nucleus  ohvaris  superior, 
lying  on  the  medial  side  of  it.  The  latter  is  the  nucleus  semi- 
lunaris. 

Nucleus  of  the  Trapezoid  Body  (N.  Corporis  Trapezoidei). — 
This  nucleus  is  deeply  imbedded  in  the  trapezoid  body  ventro- 
medial to  the  superior  oHvary  nucleus  (Fig.  88),  Its  cell-bodies 
are  scattered  and,  like  the  other  nuclei  of  the  oHvary  group,  it 
forms  a  partial  relay  for  the  auditoiy  path.  This  nucleus  is  pecu- 
liar; the  fibers  it  receives  terminate  in  the  form  of  cup-shaped  discs, 
acustic  cups,  which  are  in  direct  contact  ^^ith  its  cell-bodies  (Held). 

(2)  The  nuclei  of  the  reticular  formation  contained  in  the 
pons  are  the  n.  centralis  superior,  n.  centralis  medius,  n.  centralis 
inferior  and  n.  lateralis  medius.  All  are  microscopic.  They  are 
made  up  of  large  scattered  cell-bodies  whose  axones,  dividing  T- 
Hke,  are  both  ascending  and  descending  in  direction  (Tschermak). 
We  may  di\ide  these  axones  into  two  groups,  a  crossed  and  an 
uncrossed.     The  crossed  fibers  pierce  the  median  plane  and  become 


28o 


THE    RHOMBENCEPHALON. 


longitudinal  in  the  formatio  reticularis  near  the  ventricular  gray 
matter  and  medial  to  the  root  of  the  abducent  nerve.  At  that 
point  they  bifurcate  and  one  branch  runs  upward  and  the  other 
downward.  The  descending  branches  of  the  crossed  fibers  (lateral 
ponto-spinal  tract)  pass  through  the  substantia  reticularis  grisea 
of  the  medulla  and  the  lateral  area  of  the  spinal  cord  throughout 
its  length ;  they  end  in  the  center  of  the  gray  crescent  in  successive 
segments  until  exhausted  near  the  end  of  the  cord  (Tschermak, 


Fig.  89. — Diagram  of  a  transverse  section  through  the  junction  of  the  medulla  and 
pons  showing  the  roots  and  nuclei  of  the  eighth  cranial  nerve  and  the  auditory- 
paths  in  the  pons.     (After  Morris's  Anatomy.) 

a.  Bechterew's  nucleus,  b.  Nuc.  of  descending  root.  c.  Restiform  body.  d.  Lat. 
cochlear  nucleus,  e.  Ventral  nucleus,  f.  Vestibular  nerve,  g.  Semicircular  canals,  h. 
Cochlear  nerve,  i.  Cochlea,  j.  Dorso-lateral  nucleus  (Deitersi).  k.  Dorso-medial  nucleus. 
1.  Lateral  fillet,  m.  Superior  olivary  nucleus,  n.  Nucleus  of  trapezoid  body.  o.  Trapezoid 
body. 


Barker).  The  uncrossed  fibers  from  the  reticular  nuclei  enter 
the  medial  longitudinal  bundle  of  the  same  side  and  there  branch 
T-hke.  The  descending  branches  (anterior  ponto-spinal  tract) 
run  with  this  bundle  into  the  anterior  column  of  the  spinal  cord, 
through  which  some  of  them  continue  to  the  end.  They  occupy 
the  outer  side  of  the  anterior  funiculus  and  end  in  succession  in 
the  anterior  columna  of  gray  matter  (Tschermak  and  Barker). 
Just  what  is  the  destination  of  the  ascending  branches  of  either 
group  of  fibers  has  not  been  determined.  J.  S.  Collier  suggests 
that  these  tracts  from  the  reticular  nuclei  should  be  called  the 
crossed  and  uncrossed  ponto-spinal  tracts  (Brain,  Vol.  24,  1901). 


GRAY    MATTER    OF    THE    PONS.  281 

(3)  Nerve  Nuclei. — ^Thc  nuclei  of  ike  trigeminal  nerve  (nuclei 
ncrvi  trigcmini)  are  two  in  number.  The  genetic  or  motor  nucleus 
of  the  fifth  nerve  (n.  motorius)  in  the  pons  is  a  continuation  of  the 
mesencephalic  nucleus.  It  is  rather  close  to  the  fourth  ventricle 
in  the  extreme  lateral  part  of  its  floor,  underneath  the  locus  caeru- 
leus  (Fig.  86).  It  extends  as  far  dovm  as  the  middle  of  the  pons, 
where  the  whole  group  of  axones  passes  forward  into  the  motor 
root  of  the  nerve.  Cortical  Connection. — ^The  nucleus  receives 
motor  fibers  from  the  opposite  pyramidal  tract  and  perhaps  from 
the  cerebro-pontal  tracts  of  the  same  side;  and  sensory  fibers 
terminate  in  it  from  the  sensory  root  of  the  fifth  nerve,  and 
from  the  terminal  nuclei  of  other  common  sensory  nerves,  through 
the  medial  longitudinal  bundle  and  establish  its  reflex  connections. 

The  terminal  or  sensory  nucleus  (n.  terminalis  or  sensihilis) 
of  the  trigeminal  nerve  begins  at  the  middle  of  the  pons  and 
extends  to  the  second  segment  of  the  spinal  cord.  At  its  superior 
end  it  is  ventro-lateral  to  the  motor  nucleus  and  under  cover  of 
the  brachium  conjunctivum  of  the  cerebellum  (Figs.  86  and  87). 
Near  the  medulla  it  Kes  ventro-medial  to  the  restiform  body  and 
the  vestibular  root  of  the  acustic  nerve.  This  part  of  it  is  almost 
in  contact  with  the  nucleus  of  the  facial  nerve,  and  its  distance 
from  the  ventricle  is  greater  than  it  is  higher  up.  The  nucleus 
is  gelatinous  in  character  and  is  continuous  with  the  same  substance 
in  the  posterior  columna  of  the  spinal  cord.  It  receives  the 
whole  sensory  root  of  the  trigeminal  nerve.  Just  lateral  to  it 
runs  the  spinal  tract  of  the  fifth  nerve,  the  fibers  of  which  gradually 
bend  into  the  nucleus  and  terminate  in  rich  arborizations.  Axones 
from  the  nucleus  pursue  several  different  courses:  (a.)  Reflex 
fibers  go  directly  to  the  motor  nucleus  of  the  fifth  and  through  the 
medial  longitudinal  bundle  to  other  motor  nuclei,  (b)  Tactile, 
pain  and  temperature  fibers  are  supposed  to  enter  the  opposite 
spino-thalamic  tract  through  which  they  reach  the  thalamus; 
perhaps,  some  run  through  the  anterior  cerebello-spinal  tract 
to  the  cerebellum,  (c)  Tactile  and  muscular  sense  fibers  pro- 
ceed to  the  thalamus,  probably  through  the  medial  fillet  on  the 
opposite  side. 

Nucleus  of  the  Abducent  Nerve  {N.  Nervi  Abducent  is). —Thh 


282  THE    RHOMBENCEPHALON. 

motor  nucleus  is  close  to  the  median  plane  and  is  separated  from 
the  ependyma  of  the  ventricular  floor  only  by  the  fibers  of  the 
seventh  or  facial  nerve.  It  is  situated  in  the  colliculus  facialis 
(Figs.  86  and  88).  The  root-fibers  of  the  facial  nerve  run  lateral 
to  the  sixth  nucleus,  describe  a  loop  on  its  dorsal  surface  and  then 
return  lateral  to  it.  Cortical  Connection. — ^The  abducent  nucleus 
receives  the  end-tufts  of  motor  fibers  from  the  opposite  pyramidal 
tract  and  from  the  cerebro-pontal  tracts.  It  receives  reflex 
impulses  through  the  anterior  and  medial  longitudinal  bundles 
and  the  pedicle  of  the  superior  ohvary  nucleus;  and  perhaps,  also, 
through  the  brachium  conjunctivum  from  the  cerebellum.  The 
axones  of  the  cell-bodies  in  the  adbucent  nucleus  run  in  two  direc- 
tions: The  greater  number  run  ventro-lateralward  and  emerge 
at  the  lower  part  of  the  pons,  as  abducent  nerve;  a  small  bundle 
of  axones  runs  to  the  oculomotor  nucleus  on  the  opposite  side 
by  way  of  the  medial  longitudinal  bundle.  The  former  inner- 
vates the  external  rectus  muscle  of  the  eye  on  the  same  side  as  the 
nucleus ;  the  latter,  through  the  third  nerve,  innervates  the  internal 
rectus  of  the  opposite  eye,  though  that  muscle  receives  independent 
fibers  from  the  third,  also. 

The  nucleus  of  the  facial  or  seventh  nerve  (n.  nervi  facialis) 
is  genetic  or  motor  (Fig.  88).  It  is  situated  deep  in  the  pons,  in 
the  lateral  part  of  the  formatio  reticularis,  beneath  the  superior 
fovea.  Immediately  ventral  to  it  is  the  superior  ohvary  nucleus, 
and  the  substantia  gelatinosa  (Rolandi)  lies  dorso-lateral  to  it. 
The  nucleus  is  placed  midway  between  the  spinal  tract  of  the 
fifth  nerve  and  the  olivary  fasciculus.  Cortical  Connections. — 
It  receives  voluntary  motor  impulses  from  the  cerebral  cortex 
of  the  opposite  hemisphere  via  the  pyramidal  tract;  and,  prob- 
ably, fibers  of  the  cerebro-pontal  tracts  terminate  in  it.  These 
estabhsh  its  motor  connections.  The  rejlex  connections  of  the 
facial  nucleus  are  established  by  fibers  from  the  spinal  tract  of  the 
trigeminal  nerve,  from  the  trapezoid  body  (Cunningham),  and 
from  the  medial  longitudinal  bundle.  The  axones  of  the  cell- 
bodies  in  the  nucleus  facialis  all  enter  the  root  of  the  facial  nerve. 
By  its  direction  this  root  is  divided  into  three  parts,  viz.,  two 
distinct  parallel  parts,  joined  by  a  very  short  ascending  portion. 


GRAY    MATTER    OF    THE    PONS.  283 

(i)  The  recurrent  part,  the  pars  prima,  runs  dorso-medianward 
to  the  colHculus  faciaHs,  passing  lateral  and  then  dorsal  to  the 
lower  end  of  the  abducent  nucleus;  (2)  it  then  ascends  about  one- 
fifth  of  an  inch  (Cunningham)  between  the  ventricular  ependyma, 
dorsally,  and  the  abducent  nucleus  and  medial  longitudinal  bundle, 
ventrally,  and  this  part  is  called  the  genu  internum;  and  (3) 
the  pars  secunda,  bending  sharply  outward  over  the  nucleus  of  the 
sixth  nerve,  then  plunges  ventrally  through  the  pons ;  this  emer- 
gent part  of  the  root  runs  between  the  nuclei  of  the  facial  and 
trigeminal  nerves.  The  root  of  the  facial  nerve  is  joined  at  the 
genu  internum  by  fibers  from  the  medial  longitudinal  bundle 
which  rise  in  the  oculumotor  and  hypoglossal  nuclei  and  supply 
the  facial  muscles  above  the  orbit  and  the  orbicularis  oris  res- 
pectively. 

Just  dorsal  to  the  facial  nucleus  is  a  small  group  of  cell-bodies 
which  is  said  to  constitute  a  salivary  nucleus  (Cunningham). 
Its  axones  run  to  their  destination  through  the  nervus  inter- 
medius  and  its  chorda  tympani  branch,  and  form  the  efferent 
root  of  the  nervus  interdemedius.  They  are  secretory  and  vaso- 
dilator fibers  to  the  submaxillary  and  subhngual  glands. 

Vestibular  Nucleus  of  the  Auditory  Nerve  (N.  Nervi  Vestib- 
ularis) (Fig.  88). — This  nucleus  is  made  up  of  three  parts:  (i) 
The  chief  nucleus  (Schwalbe);  (2)  the  nucleus  of  the  descending 
root,  and  (3)  the  nucleus  of  Deiters,  which  is  lateral  in  position. 
The  superior  parts  of  Schwalbe's  and  of  Deiters's  nuclei  extend 
into  the  pons  just  medial  to  the  restiform  body,  and  the  nucleus 
of  Deiters  is  prolonged  dorsally  along  that  body  toward  the  cere- 
bellum. This  dorsal  extension  of  Deiters's  nucleus  is  called 
Flechsig's  or  Bechterew's  nucleus.  We  shall  recur  to  the  vestib- 
ular nucleus  in  the  medulla  where  the  greater  part  of  it  is  located. 

Lesions  in  the  pons  are  usually  attended  by  crossed  paralysis. 
The  paralysis  and  anaesthesia  of  parts  supphed  by  spinal  and 
by  bulbar  cerebral  nerves  are  on  the  opposite  side,  but  the  fifth, 
sixth  and  seventh  cerebral  nerves  of  the  same  side  as  the  lesion 
are  apt  to  be  involved.  If  the  spino-thalamic  and  anterior  ascend- 
ing cerebello-spinal  tracts  are  involved  and  not  the  medial  fillet, 
the  pain  and  temperature  sense  is  lost,  but  there  is  no  ataxia;  if 


284  THE    RHOMBENCEPHALON. 

the  medial  fillet  be  destroyed  and  not  the  spino-thalamic  and 
anterior  ascending  cerebello-spinal  tracts,  then  the  pain  and 
temperature  sense  is  intact,  but  the  muscular  sense  is  lost  on  the 
opposite  side  of  the  body.  The  tactile  sense  is  impaired  in  both 
cases.  A  lesion  of  the  trapezoid  body  produces  almost  total 
deafness;  of  the  lateral  fillet,  slightly  impaired  hearing  on  the 
same  side  and  nearly  complete  deafness  in  the  opposite  ear. 
Conjugate  deviation  occurs  when  the  nucleus  of  the  sixth  nerve 
is  affected;  and  strabismus  when  the  root  fibers,  but  not  the 
nucleus,  are  involved.  The  strabismus  is  external  if  the  lesion 
be  irritative  and  internal  if  the  root  fibers  are  destroyed.  Des- 
tructive lesion  in  the  nucleus  of  the  seventh  nerve  causes  inferior 
paralysis  of  the  face,  the  frontalis,  corrugator,  orbicularis  oculi 
and  orbicularis  oris  not  being  affected.  Complete  facial  paral- 
ysis occurs  if  the  root-fibers  of  the  facial  nerve  be  destroyed  in 
the  pars  secunda  or  in  the  genu  internum. 

RHOMBENCEPHALON. 

SECTION  III.     THE  MEDULLA  OBLONGATA. 
(MYELENCEPHALON.) 

Situation. — ^The  medulla  oblongata  is  the  distal,  or  caudal 
part  of  the  brain  (Figs.  21  and  27).  It  may  be  regarded  as  the 
expanded  intra-cranial  portion  of  the  spinal  cord,  hence  the 
synonym,  spinal  bulb.  It  occupies  the  basilar  groove  of  the 
occipital  bone,  posterior  to  the  pons;  and  is  continuous  with  the 
spinal  cord  below  the  foramen  magnum.  Dorsally,  it  is  in  part 
concealed  in  the  valley  of  the  cerebellum.  The  vertebral  arteries 
wind  forward  around  it,  and  form  the  basilar  at  its  jimction  with 
the  pons. 

Size. — The  medulla  is  about  an  inch  long,  and  dorso-ventrally, 
is  a  half-inch  thick.  Its  width  at  the  lower  end  is  a  half -inch,  also. 
At  the  upper  extremity  it  measures  from  three-quarters  of  an 
inch  to  one  inch  in  vddth  (Figs.  85  and  86). 

Its  shape  resembles  an  inverted  frustum  of  a  cone  flattened 
dorso-ventrally  at  the  base.  The  truncated  apex  of  the  frustum, 
which  is  nearly  circular  in  outline,  is  continuous  with  the  spinal 


THE    MEDULLA    OBLONGATA. 


285 


cord;  and  the  flattened  base  joins  the  pons.  On  the  anterior 
surface,  a  transverse  groove  marks  the  boundary  between  the 
medulla  and  pons.  The  medulla  is  a  bilateral  organ  composed 
of  symmetrical  halves  (Figs.  85  and  86).  In  the  interior,  the  two 
halves  are  united  by  both  gray  and  white  matter  in  the  raphe,  but 
on  the  surface  they  are  partially  separated  by  the  anterior  and 
the  posterior  median  fissures  (fissura  mediana  anterior  and  f. 
m.  posterior).  These  fissures  are  continued  through  the  spinal 
cord,  but  neither  extends  the  whole  length  of  the  medulla.  The 
anterior  median  fissure  is  interrupted  in  the  lower  part  of  the 
medulla  by  the  crossing  of  two  large  tracts  of  fibers,  forming  the 


Fig.  90. — Section  of  embryonic  medulla.     Length  of  back,  9.1  mm. 
(Gordinier  and  Minot  after  His.) 

RL.  Rhomboid  lip.    Ts.  Tractus  solitarius.    X.  Vagus  nerve.    XII.  Hypoglossal  ner\-e. 


decussation  of  the  pyramids;  while  only  through  the  lower  half 
of  the  medulla  does  the  posterior  median  fissure  extend. 

Origin. — ^The  medulla  oblongata  is  developed  from  the  myel- 
encephalon  of  the  embryo  (Figs.  90  and  118).  The  myelen- 
cephalic  floor  and  walls  thicken  and  form  the  greater  part  of  the 
medulla.  Inferiorly,  the  roof  undergoes  some  thickening;  but 
it  stretches  out  into  a  single  layer  of  epitheHum,  superiorly,  which 
is  continuous  at  its  upper  end  with  the  inferior  medullary  velum 
of  the  cerebellum. 

Ventricle. — ^The  common  cavity  of  the  posterior  brain  vesicle 
persists  in  the  mature  brain  as  the  fourth  ventricle  (Figs.  118, 
90  and  86).  The  fourth  is,  therefore,  the  ventricle  of  the  adult 
rhombencephalon  (see  page  313). 


286  THE    RHOMBENCEPHALON. 

SURFACES. 

The  medulla  oblongata  presents  four  surfaces:  The  anterior, 
posterior  and  two  lateral,  separated  by  the  anterior  lateral  and 
posterior  lateral  grooves.  In  the  upper  medulla,  the  surfaces  are 
clearly  defined;  but  they  become  less  distinct  as  they  descend  to 
the  inferior  and  nearly  circular  extremity  (Figs.  8i,  85  and  86). 

The  anterior  lateral  sulcus  (s.  lateralis  anterior)  separates 
the  anterior  from  the  lateral  surface, 'and  is  in  Hne  with  the  ex- 
its of  the  anterior  roots  of  the  spinal  nerves.  No  corresponding 
groove  exists  in  the  cord.  From  the  anterior  lateral  groove  issue 
the  roots  of  the  hypoglossal  nerve  and  the  anterior  root  of  the 
first  cervical  nerve.  The  abducent  (or  sixth)  nerve  rises  nearly 
in  hne  with  it  from  the  transverse  groove  between  the  pons  and 
the  medulla  (Fig.  86). 

Posterior  Lateral  Sulcus.  (5.  lateralis  posterior). — ^The  pos- 
terior lateral  sulcus  of  the  medulla  separates  the  lateral  from' the 
posterior  surface  (Figs.  86  and  87).  It  descends  between  the  olive 
and  the  restiform  body  and  is  continued  through  the  spinal  cord. 
Through  this  sulcus  into  the  cord  run  the  posterior  roots  of  the 
spinal  nerves,  and,  likewise,  the  sensory  roots  of  the  vagus  and 
glossopharyngeal  nerves  run  through  it  into  the  medulla ;  while 
the  motor  roots  of  the  ninth  and  tenth  and  the  cerebral  root  of 
the  eleventh  nerve  emerge  from  the  medulla  through  the  pos- 
terior lateral  sulcus.  The  roots  of  the  seventh,  eighth  and  inter- 
mediate nerves  are  found  at  the  superior  end  of  the  sulcus  in  the 
transverse  groove  between  the  medulla  and  pons.  The  posterior 
lateral  sulcus  is  not  parallel  with  the  axis  of  the  medulla,  but  bends 
outward  and  forward  as  it  ascends.  Inferiorly,  it  is  obhterated 
for  a  short  distance  by  the  crossing  of  the  fasciculus  cerebello- 
spinalis  (direct  cerebellar  tract)  from  the  lateral  to  the  posterior 
surface. 

The  anterior  surface  {fades  anterior)  of  the  medulla,  bounded 
on  either  side  by  the  anterior  lateral  sulcus,  extends  from  the  trans- 
verse sulcus  below  the  pons  down  to  the  spinal  cord  (Fig.  85). 
It  is  made  up  of  symmetrical  halves  united,  below,  by  the  decus- 
sation of  the  lateral  (crossed)  pyramidal  tracts;  but  separated, 
above,  by  the  anterior  median  fissure,  which  terminates  at  the 


SURFACES.  287 

inferior  end  of  the  pons  in  a  blind  foramen  (foramen  caecum  of 
Vicq  d'Azyr).  On  either  side  of  the  median  fissure,  the  ante- 
rior surface  presents  a  fusiform  eminence,  most  prominent  near 
the  pons,  called  the  pyramid.  The  pyramidal  tract,  which  we 
have  already  traced  through  the  internal  capsule,  basis  peduncuH 
and  pons,  forms  the  pyramid  of  the  medulla.  In  the  lower  part 
of  the  medulla  the  pyramid  divides  into  two  tracts,  \dz.,  the  lateral 
(or  crossed)  pyramidal  tract  and  the  anterior  (or  direct)  pyrami- 
dal tract,  the  former  comprising  about  the  medial  four-fifths  and 
the  anterior  pyramidal  tract  the  lateral  one-fifth  of  the  pyramid. 
Transverse  fibers,  called  the  anterior  external  arcuate,  are  also 
seen  crossing  the  pyramid  from  mthin  outward.  They  form  a 
more  or  less  continuous  sheet  of  fibers,  which  emerges  from  the 
anterior  median  fissure  and  winds  around  the  medulla  to  the 
posterior  surface,  w'here  its  fibers  enter  the  restiform  body.  The 
anterior  surface  is  identical  with  the  surface  of  the  two  anterior 
areas  of  the  medulla. 

Lateral  Surface.  {Fades  lateralis,  Figs.  81  and  85).— There 
are  two  lateral  surfaces,  a  right  and  a  left.  Each  is  bounded  by 
the  anterior  lateral  and  the  posterior  lateral  sulcus ;  and  is  inclosed 
between  the  roots  of  the  hypoglossal  nerve,  ventrally,  and  those 
of  the  ninth,  tenth  and  the  cerebral  portion  of  the  eleventh,  dor- 
sally.  Lateral  surface  is  synonymous  with  the  surface  of  the  lat- 
eral area.  The  lateral  surface  is  formed,  above,  by  the  olive,  beloW' , 
by  the  lateral  column  and,  winding  backw^ard  over  both,  are  the 
anterior  external  arcuate  fibers. 

The  olive  (oliva)  is  an  elongated  eminence,  a  half  inch  in 
length,  situated  just  below  the  pons  (Fig.  85).  It  is  produced 
by  the  inferior  olivary  nucleus  in  the  lateral  area  of  the  medulla; 
and,  superficially,  is  composed  of  fibers  continuous  vvith  the  fascic- 
ulus proprius  of  the  lateral  column  in  the  spinal  cord  (Fig.  93). 

Lateral  Column.  (Funiculus  lateralis.  Fig.  85). — It  is  made 
up  of  three  great  bimdles  of  fibers  (Figs.  93,  94  and  95):  The 
lateral  fasciculus  proprius,  which,  spHtting  into  a  superficial  and 
a  deep  lamina,  incloses  the  inferior  olivary  nucleus;  the  anterior 
descending  cerebellospinal  tract,  running  down  the  anterior  lateral 
sulcus;    and    the    anterior   ascending   cerebellospinal   and    spina- 


255  THE    RHOMBENCEPHALON. 

thalamic  tract,  which  runs  up  the  posterior  lateral  groove.  At 
the  junction  of  the  medulla  with  the  spinal  cord  the  cerebello- 
spinal fasciculus  (direct  cerebellar  tract)  passes  from  the  lateral 
to  the  posterior  surface.  The  anterior  external  arcuate  fibers, 
running  from  the  anterior  surface  backward  to  the  restiform  body, 
may  be  so  numerous  as  to  conceal  the  lateral  column  and  lower 
part  of  the  olive. 

The  posterior  surface  (fades  posterior)  of  the  medulla  com- 
prises all  the  surface  inclosed  between  the  diverging  posterior 
lateral  sulci  (Fig.  86).  It  embraces  the  surfaces  of  the  two  pos- 
terior areas  of  the  medulla. 

Inferiorly,  it  is  divided  into  lateral  halves  by  the  posterior 
median  fissure,  and  presents  four  bundles  of  fibers  in  each  half 
(Figs.  91,  94  and  96).  From  the  fissure  outward  they  are  as 
follows :  The  funiculus  gracilis,  funiculus  cuneatus,  tr  actus 
spinalis  n.  trigemini,  and  the  cerebello- spinal  fasciculus.  The  fun- 
iculus gracilis  (Fig.  96)  is  a  continuation  of  the  medial  tract  of 
the  posterior  column  of  the  spinal  cord,  and  the  funiculus  cune- 
atus is  in  direct  continuity  with' the  lateral  tract  in  the  same  column 
of  the  cord.  These  two  bundles  leave  the  surface  and  end  in  the 
nuclei  of  these  columns  in  the  medulla.  The  spinal  tract  of  the 
trigeminal  nerve 'is  here  situated  on  the  surface;  its  fibers  end  in 
the  under-lying  gelatinous  substance.  The  fasciculus  cerebello- 
spinalis  (direct  cerebellar  tract)  is  continued  up  from  the  lateral 
column  of  the  spinal  cord.  Remaining  on  the  surface  it  runs  up 
to  the  cerebellum  through  the  restiform  body. 

Superiorly,  the  posterior  surface,  on  either  side,  is  formed  by  a 
large  rounded  band  of  fibers,  the  restiform  body  (Figs.  91  and  96). 
The  restiform  body  (corpus  restiforme)  is  continued  upward  to 
the  pons  and  then  bends  backward  into  the  corpus  medullare  of 
the  cerebellum  in  connection  with  which  it  has  already  been 
studied.  Of  the  superficial  fibers  in  the  medulla,  the  cerebello- 
spinal fasciculus,  and  the  anterior  and  posterior  external  arcuate 
fibers  are  continued  into  the  restiform  body;  and,  as  we  have 
already  learned,  the  restiform  body  contains,  in  addition  to  the 
above  three  tracts,  the  tract  from  the  lateral  nucleus  and  the  cere- 
bello-olivary   tract.     A    single   layer  of  flattened  epithelial  cells 


SURFACES. 


289 


stretches  between  the  two  restiform  bodies,  and  roofs  over  the 
inferior  part  of  the  fourth  ventricle.  That  is  the  roof  epithelium. 
It  is  continuous  with  the  surface  layer  of  the  cpendyma  lining  the 
fourth  ventricle.     By  it  the  posterior  surface  is  completed. 

The  roof  epithelium  (Figs.  90  and  91),  seen  in  the  mid-dorsal 
surface  of  the  medulla,  is  of  triangular  shape;  its  base  is  attached 
to  the  inferior  medullary  velum  of  the  cerebellum ;  its  apex,  which 
is  directed  downward,   terminates  at  the   obex  and   covers  the 


Inferior  quadrigeminal 

coUiculus 

Fourth  nerve 


Superior  medullary 
velum 


Restiform  body 

Tffinia 

Epithelial  roof  of 

fourth  ventricle 

Cuneate  tubercle' 

Clava 

Tuberculum  cinereum 


Frenulum  veli 
Lateral/fillet 

Lingula 


Fourth 
ventricle 


Inferior  medullary 
velum 
Chorioid  plexus 

Median  aperture 
(Magendi) 

Obex 


Fig.  91. — Roof  and  lateral  walls  of  fourth  ventricle,  and  its  chorioid  plexuses. 
(After  Morris's  Anatomy.) 


inferior  angle  of  the  fourth  ventricle;  and,  laterally,  it  is  attached 
to  the  clava,  the  cuneate  funiculus  and  the  restiform  body.  The 
line  of  attachment  to  the  restiform  body  runs,  first,  obliquely 
upward  and  outward;  and  then,  transversely  outward,  inferior 
to  the  lateral  recess.  The  borders  of  the  epithelial  lamina  become 
thickened  by  the  addition  of  neuroglia,  and  are  in  continuity 
with  the  ependyma  of  the  ventricle.  The  thickened  apex  of  the 
epithelial  lamina  is  called  the  obex.  With  the  pia  mater  investing 
19 


290  THE    RHOMBENCEPHALON. 

it,  termed  the  chorioid  tela  of  the  fourth  ventricle,  this  roof  epithe- 
lium is  perforated  in  the  median  line  near  the  obex  by  a  foramen, 
the  median  aperture  {apertura  mediana  ventriculi  quarti,  Magendi) 
and  over  each  lateral  recess  by  the  lateral  aperture  {apertura 
lateralis  ventriculi  quarti,  Key  and  Retzii).  These  foramina  estab- 
lish communication  between  the  subarachnoid  space  and  the  ven- 
tricle. On  either  side  of  the  median  line  there  is  a  longitudinal 
invagination  of  the  epithelial  lamina  into  the  ventricle  and  a 
similar  transverse  one  just  below  the  inferior  medullary  velum, 
both  of  which  are  occupied  by  a  vascular  fold  of  pia  mater.  This 
fold  constitutes  the  chorioid  plexus  of  the  fourth  ventricle  (plexus 
chorioideus  ventriculi  quarti).  If  the  roof  epithelium  be  torn 
away,  as  it  usually  is  with  the  pia,  a  rough  Kne  of  separation  is 
seen  winding  over  the  restiform  body.  That  line  is  the  tcsnia 
of  the  fourth  ventricle.     Two  layers  of  ependyma  form  it. 

When  the  roof  epithelium  is  thus  removed,  the  lower  triangle 
of  the  floor  of  the.  fourth  ventricle  is  brought  into  view  (Figs. 
86  and  96).  Notice  the  median  longitudinal  furrow  bounded  by 
the  eminentice  mediates,  which  form  the  calamus  scriptorius;  then 
the  little  fossa  in  the .  sulcus  limitans,  called  the  fovea  inferior, 
situated  lateral  to  the  middle  of  the  pen,  and  the  ala  cinerea  (tri- 
gonum  vagi),  whose  superior  angle  is  formed  by  the  fovea  inferior; 
and,  last,  the  large  lateral  area,  located  above  the  ala  cinerea 
external  to  the  eminentia  medialis,  and  crossed  by  the  nearly 
transverse  medullary  strice.  This  region  is  called  the  area  acus- 
tica. 

WHITE  MATTER  OF  MEDULLA. 

The  medulla  is  made  up  of  white  and  gray  matter,  which  to- 
gether bound  ventrally  and  laterally  the  inferior  part  of  the  fourth 
ventricle,  and  surround  the  upper  extremity  of  the  sixth  ventricle 
(Figs.  92  and  95). 

For  the  most  part  the  white  matter  of  the  medulla  is  continu- 
ous with  the  longitudinal  fibers  of  the  pons  and  restiform  bodies, 
above,  and  with  the  spinal  cord,  below;  the  bulbar  roots  of  the 
eighth  to  the  twelfth  cerebral  nerves,  and  many  decussating  or 


WHITE    MATTER   OF    MEDULLA.  29 1 

commissural  fibers  of  the  reticular  substance  are  also  included  in 
the  white  substance. 

Substantia  Reticularis. — Superficially,  the  white  matter  is 
collected  into  great  bundles  of  fibers,  such  as  the  pyramids,  lateral 
column  and  restiform  body;  but,  in  the  deep  parts  of  the  medulla, 
the  white  matter  enters  into  a  great  network  called  the  substantia 
reticularis,  which  has  gray  matter  in  its  meshes  (Figs.  92  and  94). 
It  is  continuous,  above,  mth  the  reticular  formation  of  the  pons, 
and,  below,  with  the  fasciculi  proprii  of  the  spinal  cord.  The 
substantia  reticularis  contains  many  scattered  fibers,  processes 
of  its  intrinsic  neurones,  which  form  a  frequently  interrupted  and, 
for  the  most  part,  a  crossed  ascending  and  descending  tract. 
Transverse  and  obHque  fibers  are,  likewise,  numerous  in  the  retic- 
ular substance.  They  are  chiefly  the  arcuate  fibers.  The  distinct 
tracts  of  longitudinal  fibers  contained  in  it  \\ill  be  noticed  later 
(page  293).  The  gray  substance  of  the  substantia  reticularis 
is  composed  of  the  nucleus  lateralis  inferior,  the  eighth  to  the  twelfth 
cerebral  nerve  nuclei  and  the  olivary  nuclei. 

Raphe  (Figs.  92  and  94). — ^The  raphe  is,  primarily,  a  sagittal 
lamina  of  neurogHa  derived  from  the  floor-plate  of  the  myelen- 
cephalon.  It  lies  in  the  median  plane  and  joins  the  lateral  halves 
of  the  medulla  together.  It  is  very  distinct  in  the  superior  part 
of  the  medulla.  Below  the  level  of  the  olive,  it  is  entirely  obhter- 
ated  by  the  fillet  and  pyramidal  decussations.  The  raphe  is 
pierced  transversely  by  decussating  and  commissural  fibers  and 
is  traversed  dorso-ventralward  by  the  anterior  external  arcuate 
fibers. 

The  white  matter  of  the  medulla  is  divided  by  the  direction 
of  its  fibers  into  three  classes  or  systems:  (i)  Transverse  fibers; 
(2)  dorso-ventral  fibers;  and  (3)  longitudinal  fibers. 

(i)  The  transverse  fibers  of  the  medulla  are  really  more  or 
less  oblique  in  direction  and  most  of  them  are  arched.  They  in- 
clude the  fibers  of  the  following:  (a)  The  pyramidal  decussation 
(decussatio  pyramidum),  (b)  the  medial  fillet  in  the  decussatio 
lemniscorum,  (c)  the  anterior  external  arcuate  fibers  on  the  sur- 
face and,  also,  in  the  decussatio  lemniscorum,  and  (d)  the  cere- 
bello-oHvar}^  fibers.     The  pyramidal  decussation  (Fig.  95)  is  lo- 


292  THE    RHOMBENCEPHALON. 

cated  in  the  lower  half  of  the  medulla.  About  four-fifths  of  the 
pyramid  crosses  over  through  it,  and  becomes  the  lateral  pryam- 
idal  tract  of  the  spinal  cord.  The  lower  level  of  the  pyramidal 
decussation  marks  the  boundary  between  medulla  and  cord.  The 
medial  fillet,  the  anterior  and  the  posterior  external  arcuate  fibers 
all  rise  in  the  nucleus  funiculi  gracilis  and  nucleus  funiculi  cuneati. 
The  two  former  run  forward  and  cross  over  in  the  middle  of  the 
medulla,  forming  the  fillet  decussation  {decussatio  lemniscorum), 
after  which  they  separate  (Fig.  94).  The  medial  fillet  bends 
upward  and  ascends  between  the  inferior  olives,  hence  its  name 
in  the  medulla,  stratum  interolivare  lemnisci.  The  anterior  ex- 
ternal arcuate  fibers,  continuing  their  ventral  direction,  issue 
from  the  anterior  median  fissure  and  anterior  surface  of  the 
medulla  (Fig.  93),  then  arch  backward  around  the  medulla  to 
the  restiform  body,  through  which  they  enter  the  cerebellum. 
The  posterior  external  arcuate  fibers  run  through  the  restiform 
body  to  the  cerebellum  without  decussating.  The  external  arcu- 
ate fibers,  like  the  medial  fillet,  conduct  impulses  of  the  tactile 
and  muscular  senses.  The  cerebello-olivary  tract  is  a  large  one 
(Fig.  92).  It  comprises  most  of  the  internal  arcuate  fibers  of  the 
medulla.  Its  origin  is  in  the  cerebellar  cortex,  and  perhaps  in  the 
cerebellar  ganglia;  it  terminates  in  the  opposite  inferior  olivary 
nucleus.  This  tract  probably  belongs  to  the  indirect  motor  path, 
though  Cunningham  believes  it  to  be  ascending  in  direction. 

(2)  The  dorso-ventral  fibers  of  the  medulla  are  found  in  five 
situations:  (a)  In  the  median  raphe,  (b)  in  either  half  of  the  me- 
dulla between  the  anterior  and  lateral  areas,  running  in  a  linear 
series  of  ten  or  twelve  fascicles  toward  the  anterior  lateral  sulcus, 
and  (c)  in  several  bundles  not  exactly  in  linear  series,  which  run 
inward  or  outward  through  the  posterior  lateral  sulcus  between 
the  lateral  and  posterior  areas  of  each  side. 

(a)  The  dorso-ventral  fibers  of  the  raphe  are  the  anterior  exter- 
nal arcuate  fibers  (Fig.  92).  These  can  be  traced  to  the  cortex 
of  the  cerebellum  through  the  restiform  body.  Their  origin  is 
in  the  nuclei  funiculi  gracilis  and  funiculi  cuneati  (Fig.  94). 
Some  of  them  seem  to  be  interrupted  in  the  arcuate  nucleus  on 
the  anterior  surface  of  the  pyramid. 


WHITE    MATTER    OF    MEDULLA.  293 

The  root-bundles  of  the  eighth  to  the  twelfth  cerebral  nerves 
constitute  the  remaining  groups  of  dorso-ventral  fibers.  By 
them  the  medulla  is  divided  into  areas. 

(b)  The  root-bundles  of  the  hypoglossal  nerve  (Fig.  93)  run  from 
the  ventricular  gray  matter,  near  the  median  line,  ventro-lateral- 
ward  to  the  anterior  lateral  sulcus,  v^^here  they  emerge.  Inclosing 
between  them  and  the  raphe,  the  anterior  area,  they  also  separate 
it  from  the  lateral  area.  The  anterior  and  lateral  areas  are  bounded 
dorsally  by  the  thick  sheet  of  gray  matter  in  the  floor  of  the 
fourth  ventricle. 

(c)  The  vestibular  root  of  the  auditory  nerve,  the  roots  of  the 
glosso- pharyngeal  and  vagus  and  the  cerebral  root  of  the  accessory 
nerve  form  the  third  group  of  dorso-ventral  fibers  (Fig.  93). 

The  motor  fibers  of  the  ninth,  tenth  and  cerebral  part  of  the 
eleventh  nerves  take  their  origin  in  nuclei  of  the  medulla  and 
emerge  from  the  posterior  lateral  sulcus ;  while  the  sensory  fibers 
of  the  vagus,  glossopharyngeal  and  vestibular  nerves  enter  that 
sulcus  from  without  and  run  through  the  medulla  to  their  terminal 
nuclei  in  the  ventricular  gray  matter.  These  nuclei,  both  genetic 
and  terminal,  are  located  lateral  to  the  hypoglossal  nucleus. 
The  nerve  roots  rising  or  terminating  in  them  separate  the  lateral 
from  the  posterior  area.  The  posterior  area  comprises  everything 
dorsal  to  the  above  roots  of  the  eighth  to  eleventh  cerebral  nerves. 
It  thus  includes  the  gray  matter  in  the  floor  of  the  fourth  ventricle, 
called  the  stratum  nucleare. 

(3)  Longitudinal  Fibers. — In  the  medulla,  the  longitudinal 
fibers,  are  chiefly  continuations  of  the  same  in  the  pons  and  the 
restiform  bodies;  they  are  also  continuous  \vith  the  tracts  of  the 
spinal  cord.  They  can  be  best  located  by  reference  to  the  three 
areas  bounded  by  the  above  dorso-ventral  fibers,  namely,  anterior, 
lateral  and  posterior  areas,  which  are  distinctly  outlined  in  the 
upper  half  of  the  medulla  (Figs.  92  and  93). 

Longitudinal  Fibers  of  the  Anterior  Area. — The  anterior 
area  of  the  medulla  lies  betwen  the  raphe  and  the  roots  of  the 
hypoglossal  nerve,  and  between  the  anterior  surface  and  the  gray 
matter  in  the  floor  of  the  fourth  ventricle  (Figs.  92  and  93).  It 
contains  the  pyramid,  the  medial  iillct,  the  medial  and  anterior 


294  THE   RHOMBENCEPHALON. 

longitudiiKil  bundles,  the  substantia  reticularis  alba  and  two 
nuclei,  the  arcuate  nucleus  and  the  medial  accessory  olivary  nucleus. 
Excepting  that  part  forming  the  lateral  pyramidal  tract  and  the 
medial  fillet,  the  anterior  area  is  continued  in  the  anterior  column 
of  the  spinal  cord.  It  is  naturally  divided  into  a  ventral  and  a 
dorsal  part,  or  the  region  of  the  pyramid  and  the  region  of  the 
substantia  reticularis  alba. 

The  pyramid  (pyramis)  with  the  arcuate  nucleus  imbedded  in 
it  and  the  arcuate  fibers  winding  over  it,  occupies  the  ventral 
portion  of  the  anterior  area  (Figs.  92  and  94).  It  is  the  continua- 
tion of  the  pyramidal  tract  and  is  composed  of  the  axones  of 
cortical  cells  in  the  anterior  central  gyrus  of  the  cerebrum.  The 
pyramidal  tract  diminishes  in  size  as  it  descends  through  the  pons 
and  medulla,  because  some  of  its  fibers  terminate  in  ramifications 
about  the  cells  of  cerebral  nerve  nuclei.  In  the  lower  part  of  the 
medulla,  the  pyramid  breaks  up  into  the  anterior  (direct)  pyram- 
idal tract  (10  per  cent,  of  the  pyramid),  which,  descends  along 
the  anterior  median  fissure  in  the  same  side  of  the  spinal  cord; 
and  the  lateral  (crossed)  pyramidal  tract  (80  per  cent,  of  the  pyra- 
mid), which,  after  decussating  with  its  fellow  through  the  anterior 
median  fissure,  runs  down  in  the  lateral  column  of  the  opposite 
side  of  the  cord  (Fig.  95).  The  fibers  of  the  anterior  tract  cross 
in  succession  to  the  opposite  side  of  the  cord,  through  the  white  an- 
terior commissure;  and  there,  with  the  fibers  of  the  lateral  pyram- 
idal tract,  terminate  in  fibrillar  end-tufts  about  the  cell-bodies  in 
the  gray  matter.  Thus  the  pyramid  forms  a  crossed  cerebral 
tract  for  motor  cerebral  and  spinal  nerves.  A  small  number  of 
pyramidal  fibers  (10  per  cent.)  diverge  lateralward  from  the 
pyramid  in  the  medulla  and  descend  in  the  lateral  funiculus  of 
the  cord  without  decussation.  They  account  for  the  weakness 
on  the  well  side,  and  for  slight  motion  on  the  paralyzed  side, 
which  are  commonly  observed  in  hemiplegia.  If,  as  E.  A.  Schafer 
claims,  the  fibers  of  the  pyramidal  tracts  end  in  the  posterior 
columna  of  gray  matter,  then  at  least  one  neurone  intervenes 
between  them  and  the  motor  neurones  of  the  spinal  nerves;  but 
without  doubt,  they  enter  into  either  direct  or  indirect  relations 
with  those  neurones. 


WHITE    MATTER    OF    MEDULLA. 


295 


The  dorsal  part  of  the  anterior  area  is  occupied  by  the  substan- 
tia reticularis  alba  (Figs.  92  and  93).  It  contains  the  bodies 
of  very  few  nerve  cells  and  is  of  a  light  color.  The  medial  acces- 
sory olivary  nucleus  is  imbedded  in  it  near  the  pyramid  and  among 
the  fibers  of  the  fillet;  and  three  definite  bundles  of  longitudinal 


Fig.  92. — Section  of  medulla  oblongata  near  the  pons.     {Original.) 

a.  Hypoglossal  nucleus,  b.  Vestibular  nucleus,  c.  Tractus  solitarius.  d.  Restiform 
body.  e.  Substantia  reticularis,  f.  Hilus  of  olivary  nucleus  containing  cerebello-olivary 
fibers,  g.  Anterior  lateral  sulcus,  h.  Pyramid,  i.  Anterior  median  fissure,  j.  Anterior 
longitudinal  bundle,  k.  Medial  longitudinal  bundle.  1.  Nuc.  tractus  spinalis  n.  trigemini. 
m.  Tractus  spinalis  n.  trigemini.  n.  Lateral  cochlear  nucleus,  o.  Ventral  cochlear  nucleus. 
p.  Ascending  anterior  cerebello-spinal,  spino-thalamic,  and  rubro-spinal  tracts,  q.  Posterior 
lateral  sulcus,  r.  Medial  fillet,  interolivary  stratum,  s.  Anterior  ex.temal  arcuate  fibers. 
t.  Arcuate  nucleus. 


fibers  have  been  demonstrated  in  it,  namely,  the  medial  fillet 
and  the  medial  and  anterior  longitudinal  bundles. 

Medial  Fillet  {Lemniscus  Medialis). — Just  dorsal  to  the  pyramid 
in  the  anterior  area  of  the  medulla  at  the  level  of  the  olives,  is  a 
large  bundle  of  fibers  called  the  interolivan,'  stratum  of  the  fillet 


296  THE    RHOMBENCEPHALON. 

(Figs.  92  and  94).  Situated  between  the  inferior  olivary  nuclei, 
it  is  on  that  account  so  named.  Superiorly,  it  is  continued  as  the 
medial  fillet.  The  medial  fillet  rises  from  the  nucleus  funiculi 
gracilis  and  nucleus  funiculi  cuneati  of  the  medulla  and  crosses 
through  the  median  raphe  in  the  fillet  decussation.  As  the  fillet 
runs  brain-ward,  it  receives  fibers  from  the  terminal  nuclei  of 
common  sensory  cerebral  nerves  and  from  the  vestibular  nuclei. 
Along  its  lateral  border,  it  is  accompanied  for  a  short  distance 
in  the  pons  by  the  lateral  fillet.  The  medial  fillet  is  composed 
of  ascending  axones  which  constitute  a  "cerebral"  tract  for  the 
sensory  fibers  of  spinal  and  cerebral  nerves.  It  carries  ordinary 
sensations  (tactile  and  muscular)  to  the  superior  quadrigeminal 
coUiculus  by  the  superior  fillet,  and  to  the  thalamus  by  the  greater 
part  of  the  medial  fillet. 

The  medial  longitudinal  bundle  (fasciculus  longitudinalis 
medialis)  (Figs.  92  and  95)  which  we  have  studied  in  the  mid- 
brain and  pons,  constitutes  a  very  distinct  strand  in  the  superior 
half  of  the  medulla ;  but  below  the  level  of  the  ohve  it  can  be  identi- 
fied in  the  anterior  fasciculus  proprius  only  by  a  study  of  its 
medullation  or  of  its  degeneration.  It  is  continuous  with  the 
anterior  fasciculus  proprius  of  the  spinal  cord.  Its  location  is 
next  the  median 'raphe  and  the  ventricular  gray  substance,  imme- 
diately anterior  to  the  hypoglossal  nucleus,  in  the  upper  medulla. 
The  same  position  is  occupied  by  it  in  the  mid-brain  and  pons. 
It  is  here  in  the  medulla  that  the  hypoglossal  fibers  are  supposed 
to  enter  it  and  run  up  to  the  colliculus  facialis,  where  they  join 
the  facial  nerve  at  the  internal  genu.  At  the  middle  of  the  medulla 
the  decussation  of  the  fillet  pushes  this  bundle  forward  and  some- 
what away  from  the  median  plane,  so  that  it  runs  between  the 
fillet  decussation  and  the  medial  accessory  olivary  nucleus.  Below 
the  level  of  the  fillet  decussation  it  runs  between  the  decussatio 
pyramidum  and  the  isolated  head  of  the  anterior  columna  of  gray 
substance.  Rising  primarily  in  the  gray  matter  of  the  cord,  the 
ascending  part  of  the  medial  longitudinal  bundle  is  augmented 
in  the  medulla  and  pons  by  fibers  from  the  terminal  nuclei  of  sen- 
sory cerebral  nerves.  Most  of  its  ascending  fibers  cross  the 
median  line  and  terminate  in  the  motor  cerebral  nuclei  on  the 


WHITE    MATTER    OF    MEDULLA. 


297 


opposite  side;  these  form  the  middle  Hnks  in  many  reflex  arcs; 
a  few  decussate  in  the  posterior  commissure  and  end  in  the  thala- 
mus.    The  latter  are  sensory  conduction  fibers.     The  descending 


Fig.  93. — Section  of  the  medulla  oblongata  at  the  middle  of  olive.     {Original.) 

a.  Nucleus  of  12th  n.  b.  Vestibular  nucleus,  c.  Tractus  solitarius.  d.  Nucleus  am- 
biguus.  e.  Tractus  spinalis  n.  trigemini.  f.  Media)  accessory  olivary  nuclei,  g.  Posterior 
lateral  sulcus,  h.  Ant.  external  arcuate  fibers,  i.  Fasciculus  proprius.  j.  Arcuate  nucleus. 
k.  Anterior  longitudinal  bundle  in  substantia  reticularis  alba.  1.  Medial  longitudinal  bundle. 
m.  Nucleus  alse  cinerea.  n.  Taenia  of  4th  ventricle,  o.  Restiform  body.  p.  Gelatinous 
substance,  q.  Substantia  reticularis  grisea  nucleus  lateralis  inferior,  r.  Ascending  ant. 
cerebello-spinal,  spino-thalamic,  and  rubro-spinal  tracts,  s.  Dorsal  accessory  olivary  nu- 
cleus,   t.  Inferior  olivary  nucleus,    u"  Pyramid,     v.  Medial  fillet,  interolivary  stratum. 

part  of  the  medial  longitudinal  bundle  is  the  medial  ponto-spinal 
tract  of  Collier  (see  pages  280,  360  and  373). 

The  anterior  longitudinal  bundle  (Figs.  92  and  95)  descends 
as  a  distinct  strand,  from  the  opposite  superior  colliculus  of  the 


298  THE    RHOMBENCEPHALON. 

corpora  quadrigemina,  to  the  lower  part  of  the  medulla;  there  it 
approaches  the  medial  longitudinal  bundle  and  is  continued  along 
the  fissural  surface  of  the  anterior  column  in  the  cord.  Its  ter- 
mination is  in  the  central  gray  substance,  chiefly  the  cilio-spinal 
centers.  It  forms  the  middle  link  in  the  visual  reflex  arc.  Its 
bulbar  and  spinal  portions  constitute,  chiefly,  the  pupillo-dilator 
tract  (see  pages  158,  276  and  355). 

Longitudinal  Fibers  of  the  Lateral  Area. — ^The  contents 
of  the  lateral  area  (Figs.  92  and  93)  are  as  follows:  Superficially, 
the  lateral  fasciculus  proprius,  the  anterior  descending,  and  the 
anterior  ascending  cerebello-spinal  tracts  and  the  spino-thalamic 
tract.  Deeply,  lies  the  substantia  reticularis  grisea.  Imbedded 
in  the  substantia  reticularis  are  the  nucleus  ambiguus,  the  nucleus 
lateralis  inferior  and  the  accessory  olivary  nuclei,  and  in  the 
fasciculus  proprius  is  the  main  inferior  olivary  nucleus.  The 
gray  matter  of  the  substantia  reticularis  grisea  is  a  part  of  the 
disintegrated  anterior  columna  of  the  cord  and,  unlike  that  of 
the  anterior  area,  it  contains  the  bodies  of  many  large  nerve 
cells. 

Lateral  Fasciculus  Proprius  (Fasciculus  Lateralis  Pro- 
prius, Figs.  93  and  94). — ^The  whole  lateral  column  of  the  spinal 
cord,  except  the  lateral  pyramidal  and  cerebello-spinal  tracts,  is 
continued  into  the  lateral  area  of  the  medulla.  Composed  of  as- 
cending and  descending  axones  which  are  commissural  and  asso- 
ciative for  different  segments  of  the  spinal  cord,  the  lateral  fascic- 
ulus proprius  ascends  into  the  lateral  area  of  the  medulla,  and 
runs  in  part  beneath  and  in  part  superficial  to  the  inferior  olivary 
nucleus;  beyond  the  olive,  it  is  continued  in  the  substantia  reticu- 
laris grisea  of  the  medulla  and  reticular  formation  of  pons  and 
mid-brain.  Among  the  fibers  of  the  lateral  fasciculus  proprius, 
ventral  to  the  olive,  is  the  triangular  tract  of  Helvdg  and,  dorsal 
to  the  olive,  the  olivary  bundle.  The  former  is  believed  to  rise  in 
the  olive  of  the  medulla  and  the  latter  to  end  in  it.  They  are 
made  up  of  descending  axones  and,  according  to  Bechterew,  form 
a  functionally  continuous  tract. 

The  anterior  descending  cerebello-spinal  tract  (fasciculus 
descendens  cerebello-spinalis  anterior)  rises  in  the  cerebellar  ganglia 


WHITE    MATTER    OF    MEDULLA.  299 

and  cortex.  Between  the  cerebellum  and  the  medulla  it  comprises 
the  acustico-cercbellar  tract  and,  possibly,  the  cerebello-olivary 
tract;  and,  therefore,  is  almost  completely  relayed  in  the  vestib- 
ular nuclei,  the  nuclei  of  the  reticular  formation,  and,  possibly, 
in  the  inferior  oHvary  nucleus  (Figs.  94  and  95).  It  forms  part 
of  the  brachium  pontis  and  restiform  body  through  which  it  reaches 
the  medulla.  In  the  lateral  area,  it  descends  along  the  anterior 
lateral  sulcus,  to  the  corresponding  area  of  the  cord.  It  ends 
( ?)  in  the  anterior  columna  of  gray  matter.  It  was  once  regarded 
as  a  part  of  the  anterior  pyramidal  tract.  The  anterior  descending 
cerebello-spinal  tract  forms  a  segment  of  the  indirect  motor  path, 
and  the  motor  arm  of  the  reflex  arc  of  coordination  and  equil- 
ibrium. 

Anterior  Ascending  Cerebello-spinal  and  Spino-thalamic 
Tract.  {Fasciculus  ascendens  cerebello-spinalis  anterior)  (Figs. 
92  and  95). — ^These  two  tracts  are  combined  into  one  throughout 
the  cord,  medulla  and  pons.  Near  the  isthmus  the  former  turns 
backward  through  the  superior  medullary  velum  and  ends  in  the 
cortex  of  the  superior  vermis  cerebelli;  while  the  spino-thalamic 
tract  continues  in  the  original  direction,  to  the  lateral  nucleus 
of  the  thalamus.  The  common  spino-encephalic  tract  made 
up  of  these  two  bundles  takes  its  origin  from  the  base  of  the 
anterior  columna  and  center  of  the  crescent  of  gray  matter,  chiefly 
on  the  opposite  side  of  the  spinal  cord;  and,  crossing  through 
the  white,  anterior  commissure,  it  ascends,  mingled  somewhat 
with  the  fibers  of  the  above  descending  cerebello-spinal  tract, 
along  the  lateral  surface  of  the  cord  (Barker).  It  runs  beneath 
the  posterior  lateral  groove  of  the  medulla  and  through  the 
formatio  reticularis  of  the  pons,  to  the  point  of  division  near 
the  isthmus  rhombencephali,  whence  the  two  divisions  proceed 
to  their  cerebellar  and  thalamic  terminations,  as  above  stated. 
The  tract  is  probably  reinforced  in  the  medulla  and  pons  by  the 
addition  of  axones  from  the  opposite  terminal  nuclei  of  common 
sensory  cerebral  nerves;  and,  rising  primarily  in  relation  with  the 
posterior  roots  of  spinal  nerves,  it  thus  forms  a  crossed  path  for 
common  sensations,  spinal  and  cerebral.  It  conducts  tactile, 
pain  and  temperature  impulses  (see  pages  161  and  356). 


300  THE    RHOMBENCEPHALON. 

The  rubro-spinal  tract  is  the  crossed  descending  tract  of 
the  red  nucleus  (Figs.  92  and  95).  Running  dorsal  to  the  infe- 
rior olive  in  the  medulla  it  mingles  with  the  fibers  of  the  anterior 
ascending  cerebello-spinal  tract.  It  is  continued  down  the  cord, 
in  the  lateral  column,  to  the  lateral  columna  and  center  of  the 
gray  crescent  as  far  as  the  first  lumbar  segment  (see  pages  162, 
276  and  358). 

Longitudinal  Fibers  of  the  Posterior  Area. — ^The  longitudi- 
nal fibers  of  the  posterior  area  form  many  bundles ;  and  the  bundles 
are  different  in  upper  and  lower  medulla.  The  substantia  reticularis 
is  small.     The  ventricular  gray  substance  belongs  to  this  area. 

The  lower  medulla  contains:  The  funiculus  gracilis,  funic- 
ulus cuneatus,  tractus  spinalis  nervi  trigemini  and  cerebello- 
spinal tract,  named  from  the  posterior  median  fissure  outward 
(Figs.  94  and  96).  In  the  upper  medulla  are:  The  restiform 
body  and  the  spinal  tract  of  the  fifth  cerebral  nerve  at  the  surface ; 
and  the  tractus  solitarius  in  the  interior  (Figs.  92,  93  and  96). 

The  funiculus  gracilis  is  the  superior  end  of  the  ascending 
postero-medial  column  (Goll's  column)  of  the  spinal  cord.  Near 
its  extremity  it  expands  and  forms  the  clava,  and  then  tapers  off 
and  disappears  along  the  side  of  the  fourth  ventricle.  The  clava 
is  due  to  the  nucleus  funiculi  gracilis,  in  which  the  fibers  of  the 
column  end.  The  funiculus  gracilis  is  composed  of  ascending 
branches  of  the  posterior  roots  of  the  spinal  nerves,  which  enter 
the  cord  below  the  seventh  or  eighth  thoracic  segment. 

Funiculus  Cuneatus  (Figs.  94  and  96). — ^It  is  separated  from 
the  posterior  median  fissure  by  the  gracile  bundle;  and  is  the 
continuation  of  the  ascending  postero-lateral  column  (Burdach's 
column)  of  the  spinal  cord.  It  ends  about  the  cells  of  the  nucleus 
funiculi  cuneati  and  accessory  nucleus  funiculi  cuneati,  which 
form  the  cuneate  tubercle  seen  on  the  surface.  The  fibers  of  the 
funiculus  cuneatus  are  ascending  branches  of  the  posterior  roots 
of  the  spinal  nerves.  The  nerves  contributing  to  this  column 
are  the  cervical  and  the  six  or  eight  upper  thoracic.  The  funiculi 
gracilis  and  cuneatus  carry  to  the  nuclei  of  these  columns  common 
sensations  belonging  to  the  tactile  and  muscular  senses.  Inter- 
ference with  these  tracts  produces  ataxia. 


WHITE    MATTER    OF    MEDULLA.  3OI 

Spinal  Tract  of  the  Trigeminal  Nerve.  {Tracius  spinalis  nervi 
Irigcmini,  P'igs.  92  and  96). — It  forms  a  narrow  strip  of  the  pos- 
terior surface  of  the  medulla,  which  is  broadest  near  the  restiform 
body  and  tapers  downward  toward  the  spinal  cord.  It  is  composed 
of  the  descending  fibers  from  the  sensory  root  of  the  trigeminal 
nerve:  the  sensory  fibers  of  this  nerve  on  entering  the  pons  divide 
T-like,  into  an  ascending  and  a  descending  branch,  and  the  de- 
scending branches  form  the  spinal  tract  of  the  nerve,  which  for  a 
short  distance  is  visible  on  the  surface  of  the  medulla.  This 
tract  is  continued  through  two  segments  in  the  spinal  cord.  The 
nucleus  of  the  spinal  tract  of  the  trigeminal  nerve,  over  which  it 
runs  and  in  which  it  terminates,  is  but  the  continuation  of  the  gelat- 
inous substance  of  the  posterior  columna  of  gray  matter  in  the  cord ; 
in  the  upper  medulla  it  is  situated  ventro-medial  to  the  restiform 
body.  The  nucleus  produces  a  slight  eminence  below^  the  level 
of  the  clava,  called  the  tuberculum  cinereum. 

The  cerebello-spinal  tract  (jasciculus  cerebello-spinalis,  Figs. 
94  and  96)  in  the  lower  medulla  crosses  the  posterior  lateral 
groove  and  the  spinal  tract  of  the  fifth  nerve,  going  from  the  lateral 
column  of  the  cord  to  the  posterior  area  of  the  medulla;  it  then 
ascends  to  form  a  considerable  part  of  the  restiform  body.  It 
takes  its  origin  from  the  nucleus  dorsalis  (Clarki)  in  the  spinal 
cord.  It  ends,  very  largely  on  the  opposite  side,  in  the  cortex 
of  the  superior  cerebellar  worm.  The  cerebello-spinal  tract 
(direct  cerebellar  tract)  probably  conducts  common  sensory  im- 
pulses received  from  viscera.  They  should  be  classed  largely 
under  the  muscular  sense,  as  they  seem  to  concern  equilibrium 
and  orientation.     They  are  sympathetic  sensory. 

Restiform  Body.  (Corpus  restijorme).- — In  the  upper  medulla, 
forming  the  lateral  part  of  each  posterior  area,  is  a  large  rounded 
bundle  of  fibers,  called  the  restiform  body  (Figs.  92,  93  and  96). 
It  is  the  largest  bundle  in  the  medulla,  and  joins  it  to  the  cerebel- 
lum. It  is  made  up  of  the  following:  Ascending  tracts — (i)  the 
cerebello-spinal  tract;  (2)  the  external  arcuate  fibers,  anterior 
and  posterior;  and  (3)  the  tract  from  the  lateral  nucleus  of  the 
medulla  to  the  cortex  of  the  cerebellum.  Descending  tracts — 
(4)  the  cerebello-olivary  fibers;  and  (5)  a  few  axones  of  Purkin- 


302  THE    RHOMBENCEPHALON. 

je's  cells  which  enter  into  the  descending  cerebellar  tract  (?) 
(see  cerebellum,  page  264). 

The  restiform  body  is  inclosed  between  the  vestibular  and  coch- 
lear roots  of  the  auditory  nerve  (eighth)  (Fig.  89).  Ventral  to 
it  and  between  the  roots,  is  the  ventral  part  of  the  cochlear  nu- 
cleus ;  on  its  lateral  surface  and  among  the  fibers  of  the  lateral 
root,  is  the  dorsal,  or  lateral  part  of  the  same  nucleus.  The  ves- 
tibular nuclei — the  chief  dorso-medial  nucleus  (Schwalbe),  the 
dorsolateral  (Deiters),  the  superior  (Flechsig  and  Bechterew)  and 
the  nucleus  of  the  descending  root  are  situated  dorsal  and  medial 
to  the  restiform  body. 

Tractus  Solitarius  (Figs.  92  and  94). — ^The  solitary  tract  is  a 
small,  round  bundle  imbedded  in  the  middle  of  the  ventricular 
gray  matter  of  the  posterior  area.  In  Weigert-Pal  sections  of 
the  upper  medulla  it  is  clearly  visible  to  the  naked  eye.  It  is 
formed  by  the  sensory  roots  of  the  nervus  intermedins  and  the 
ninth  and  tenth  cerebral  nerves.  It  descends  through  the  nu- 
cleus tractus  solitarii  lateral  to  the  nucleus  of  the  ala  cinerea,  and 
along  the  medial  aspect  of  the  posterior  columna  of  gray  matter 
in  the  cord.  It  ends  on  both  sides  of  the  median  line  in  gelat- 
inous gray  matter,  called  the  nucleus  of  the  solitary  tract,  which 
surrounds  it.  The  nuclei  of  these  tracts  converge  downward; 
according  to  Cajal,  they  are  united  near  their  inferior  extremities 
by  a  central  mass,  called  the  nucleus  commissuralis  (Barker). 
The  solitary  tract  may  be  traced  from  the  upper  part  of  the  me- 
dulla down  to  the  spinal  cord  (KoUiker).  It  is  believed  to  asso- 
ciate the  nuclei  of  the  nerves  controlling  respiration,  hence  the 
synonym,  respiratory  bundle. 

GRAY  MATTER  OF  MEDULLA. 

The  gray  matter  of  the  medulla  is  composed  (i)  of  that  continu- 
ous with  the  nucleus  pontis,  called  the  arcuate  nucleus;  (2)  of  the 
ventricular  gray  substance,  the  stratum  nucleare,  and  that  of  the 
substantia  reticularis,  also  continued  downward  from  the  pons; 
and  (3)  of  the  special  nuclei  of  the  medulla,  which  are  not  repre- 
sented in  the  pons  or  in  the  spinal  cord. 

(i)  Nucleus  of  the  External  Arcuate  Fibers  (Figs.  92  and 


GRAY   MATTER    OF   MEDULLA.  303 

93). — ^This  is  the  nudes  arciialus.  It  forms  a  large  crescentic 
mass  on  the  ventral  and  medial  surface  of  the  pyramid.  Run- 
ning over  and  through  it  there  are  the  anterior  external  arcuate 
fibers,  for  certain  of  wliich  it  constitutes  a  relay.  The  arcuate 
nucleus  is  continuous  above  with  the  nucleus  pontis.  It  is  brought 
to  the  surface  at  the  lower  border  of  the  pons  by  the  disappear- 
ance of  most  of  the  transverse  fibers. 

(2)  The  gray  substance  in  the  substantia  reticularis  and  in 
the  immediate  floor  of  the  fourth  ventricle  (Figs.  92  and  93) 
is  continuous  with  the  same  in  the  pons  and  mid-brain,  above; 
and  is  represented  in  the  spinal  cord  by  the  H-shaped  column 
of  gray  matter.  By  the  posterior  and  lateral  expansion  of  the 
neural  canal,  in  the  upper  half  of  the  medulla  and  in  the  pons, 
which  forms  the  fourth  ventricle,  the  posterior  columnse  of  the 
H-shaped  column  of  gray  matter  are  pushed  outward  to  a  trans- 
verse direction;  and  the  entire  bases  of  the  anterior  columnas  are 
brought  into  the  floor  of  the  ventricle.  The  expansion  of  the  canal, 
together  with  the  decussation  of  the  lateral  pyramidal  tracts  through 
the  anterior  columnas  and  of  the  medial  fillets  through  the  pos- 
terior and  anterior  colunmse,  disposes  the  H-shaped  column  as 
follows : 

Anterior  Columna. — ^From  the  base  of  the  anterior  columna  is 
derived  a  column  of  cells,  the  hypoglossal  nucleus  (Figs.  92  and  93), 
which  is  two-thirds  of  an  inch  in  length  and  extends  along  the 
median  raphe  in  the  upper  medulla,  beneath  the  eminentia  media- 
lis.  It  is  continued  into  the  lower  medulla  as  far  as  the  pyram- 
idal decussation.  By  commissural  fibers  it  is  joined  to  the  nu- 
cleus of  the  opposite  side  according  to  Kolliker.  The  nucleus 
gives  origin  to  the  hypoglossal  nerve  proper;  and  probably  to  a 
small  fasciculus  which  by  way  of  the  medial  longitudinal  bundle 
joins  the  facial  nerve  and  supphes  the  orbicularis  oris.  The 
hypoglossal  axones  rim  in  linear  series  forward  through  the  me- 
dulla to  the  anterior  lateral  sulcus,  whence  they  emerge  between 
the  pyramid  and  the  olive  (Fig.  85).  They  separate  the  anterior 
from  the  lateral  area.  The  main  body  of  the  anterior  columna 
is  broken  up  into  the  nucleus  lateralis  inferior,  the  nucleus  ambig- 
uus  and  the  motor  part  of  the  nucleus  of  the  ala  cinerea. 


304  THE    RHOMBENCEPHALON. 

The  nucleus  lateralis  inferior  (Figs.  92  and  94)  is  situated  in 
the  reticular  substance  of  the  lateral  area.  Though  it  is  made 
up  of  large  cell-bodies,  they  are  so  scattered  among  the  fibers  of 
this  region  that  the  nucleus  is  invisible  to  the  naked  eye.  It  prob- 
ably gives  origin  to  descending  fibers  which  are  continued  both 
in  the  anterior  and  lateral  column  of  the  spinal  cord  (Tschermak). 
It  is  known  to  receive  fibers  from  the  anterior  ascending  cerebello- 
spinal tract  and  from  the  nuclei  funiculi  gracilis  and  funiculi 
cuneati,  and  it  gives  rise  to  the  ascending  tract  already  traced  to 
the  cerebellum,  which  probably  transmits  tactile,  muscular,  pain 
and  temperature  impressions  to  the  cerebellar  cortex. 

The  nucleus  ambiguus  (Fig.  93)  forms  an  irregular  sheet  of 
gray  substance,  pear-shaped  in  section,  which  extends  longitu- 
dinally through  two-thirds  of  the  medulla.  It  is  prolonged  from 
near  the  ventricle  ventro-lateralward  into  the  substantia  reticu- 
laris. It  is  not  visible  to  the  naked  eye.  Its  axones  form  the 
cerebral  root  of  the  eleventh  nerve  and  probably  a  part  of  the  motor 
roots  of  the  tenth  and  ninth  nerves.  The  root  fibers  of  the  acces- 
sory nerve  run  out  through  the  posterior  lateral  sulcus  below  the 
level  of  the  olive. 

The  nucleus  of  the  ala  cinerea  (Fig.  93)  is  in  part  derived  from 
the  base  of  the- anterior  columna;  this  part  is  motor  in  func- 
tion and  its  neurones  resemble  those  of  the  anterior  columna  in 
the  cord.  It  belongs  to  the  ninth  and  tenth  nerves.  It  is  situated, 
above,  close  to  the  floor-ependyma  of  the  fourth  ventricle  under 
the  ala  cinerea;  and  it  extends,  inferiorly,  into  the  closed  medulla 
nearly  as  far  as  the  hypoglossal  nucleus.  It  is  immediately  lateral 
to  the  nucleus  of  the  hypoglossal.  Its  axones  run  in  a  curve, 
convex  toward  the  median  plane,  between  the  restiform  body 
and  the  olive.  They  are  joined  medially  by  those  axones  of  the 
nucleus  ambiguus  which  enter  the  roots  of  the  ninth  and  tenth 
nerves.  By  this  nucleus  and  the  nucleus  ambiguus,  many  dis- 
tinct fascicles  are  formed,  belonging  to  the  roots  of  the  ninth,  tenth 
and  the  cerebral  part  of  the  eleventh  nerves.  They  run  in  slightly 
different  planes,  but  all  of  them  emerge  in  the  region  of  the  posterior 
lateral  sulcus  of  the  medulla  (Fig.  85).  Intermingled  with  the 
motor  cells  of  the  nucleus  alas  cinereae,  there  are  the  small  spindle 


GRAY    MATTER    OF    MEDULLA. 


305 


cells  of  the  terminal  nucleus  of  the  vagus  nerve,  which  represent 
neurones  of  the  posterior  columna  of  gray  matter.  They  receive 
the  end-tufts  of  the  sensory  root  fibers  of  the  vagus  nerve  and 
possibly  of  a  small  number  from  the  glossopharyngeal  nerve. 

The  hypoglossal  nucleus,  the  motor  part  of  the  nucleus  of  the 
ala  cinerea  and  the  nucleus  ambiguus  receive  many  fibers  from  the 
opposite  pyramidal  tract,  and  probably  from  the  cerebro-pontal 
tracts,  which  bring  to  them  voluntary  motor  and  inhibitory  im- 


Funiculus  gracilis  and  nucleus  Central  gray  substance 

Funiculus  cuneatus  and  nucleus          '  \      Commissural  nucleus  between  solitary 

Tractus  spinalis  n.                                  .           f  I       I                 Central  canal                          [tracts 
trigemini  and  nuc 


(Post.)  cere- 
bello-spinal 
tract 


Anterior  cere- 
bello-spinal, 
spino-thalamic 

and  triangular  tracts  /  "^\7 

Inferior  olivary  nucleus 

Medial  accessory  olivary  nuc. 


Medial  and  an- 
terior longitu- 
dinal bundles 

Ascending  Ant. 
cerebello- 
spinal, spir.o- 
thalamac  and 
rubrc  spinal 
tracts 

Triangular 
tract  (Helwigi) 


Descending  ant.   cerebello- 
Medial  fillet  spinal  tract 

Fillet  decussation 


Fig-  94-— Section  of  the  medulla  oblongata  at  the  fillet  decussation.     (Original.) 


pulses  from  the  cerebral  cortex;  and  their  reflex  connection  is  estab- 
Hshed  by  fibers  of  the  medial  longitudinal  bundle  which  rise  in 
sensory  nuclei. 

The  posterior  columna  is  decapitated  by  the  fillet.  It  is  repre- 
sented in  the  medulla  (i)  by  the  following  terminal  nuclei,  viz., 
the  sensory  part  of  the  nucleus  alae  cinereas  of  the  vagus  and 
glossopharyngeal  nerves,  the  vestibular  and  cochlear  nuclei  of 
the  auditory  nerve,  the  nucleus  tractus  solitarii  and  the  nucleus 
of  the  spinal  tract  of  the  trigeminal  nerve;  and  (2)  by  the  gray 
matter  of  the  reticular  substance  of  the  posterior  area. 


3o6  THE    RHOMBENCEPHALON. 

T?he  nucleus  alee,  cinerecs.  of  the  vagus  and  glossopharyngeal 
nerves  (Fig.  93)  contains  in  its  lateral  part  a  group  of  small  fusi- 
form cell-bodies  like  those  in  the  posterior  columna.  These 
fusiform  cells  constitute  the  terminal  nucleus  of  the  sensory  fibers 
of  the  vagus,  and  it  is  probable  that  a  few  glossopharyngeal  fibers 
also  arborize  and  end  in  the  nucleus.  Cortical  Connection. — 
Axones  of  this  nucleus  probably  enter  into  the  medial  fillet,  the 
spino-thalamic  tract  and  the  medial  longitudinal  bundle.  The 
two  former  conduct  tactile,  muscular,  pain  and  temperature  impul- 
ses to  the  thalamus,  whence  the  cortical  fillet  carries  them  to  the 
cortex;  the  latter  establishes  its  reflex  connection  with  motor 
nerves. 

Nucleus  Tr actus  Solitarii  (Figs.  92  and  94), — ^The  nucleus  of 
the  soHtary  tract  surrounds  the  tractus  sohtarius  with  which  it 
coincides  in  extent.  It  is  gelatinous  in  appearance  and  is  situated 
just  lateral  to  the  nucleus  of  the  ala  cinerea.  In  its  descent  it 
trends  dorsaUy  and  toward  the  median  fine.  It  is  joined  to  the 
opposite  nucleus,  at  its  spinal  end,  by  the  nucleus  commissuralis 
(Cajal).  The  nucleus  of  the  sohtary  tract  is  the  terminal  nucleus 
of  the  afferent  fibers  of  the  intermediate  and  glossopharyngeal 
nerves  and,  probably,  receives  a  few  fibers  from  the  vagus.  It  is 
thus  the  nucleus  of  the  nerves  of  taste  and  forms  the  first  relay 
station  in  the  gustatory  path.  The  axones  of  the  ceU-bodies  in 
the  nucleus  tractus  sohtarii  establish  reflex  connections  with  effer- 
ent nuclei  and  continue  the  taste  path  toward  the  thalamus,  but 
their  exact  course  has  not  been  worked  out. 

Nucleus  Tractus  Spinalis  Nervi  Trigemini  (Figs.  92  and  95). — 
The  nucleus  of  the  spinal  tract  of  the  trigeminal  nerve  is  gelatinous 
in  character.  It  is  continuous  \Aith  the  sensory  pontine  nucleus 
of  the  trigeminal  nerve,  above;  and,  below,  is  continued  in  the 
gelatinous  substance  of  the  posterior  columna  of  the  spinal  cord. 
As  low  down  as  the  second  cervical  segment  it  receives  fibers 
from  the  trigeminal  nerve,  so  the  terminal  nucleus  of  this  nerv^e 
extends  from  the  middle  of  the  pons  to  the  second  cervical  nerve. 
The  nucleus  of  the  trigeminal  is  embraced  between  the  emergent 
part  of  the  facial  nerve,  medially,  and  the  vestibular  ner\^e,  later- 
ally, in  the  lower  portion  of  the  pons;  in  the  upper  medulla,  the 


GRAY   MATTER    OF   MEDULLA.  307 

nucleus  lies  along  the  ventro-medial  surface  of  the  restiform  body ; 
it  enlarges  in  bulk  and  approaches  the  surface  near  the  middle 
of  the  medulla,  where  it  produces  the  tuberculum  cinereum; 
and  it  is  then  continued  dowoi  into  the  cord  as  a  cap  of  the  poste- 
rior columna  of  gray  substance.  In  the  lower  part  of  the  medulla 
the  nucleus  underHes  the  visible  part  of  the  tractus  spinahs  nervi 
trigemini. 

The  sensory  root  of  the  trigeminal  nerve  (fifth)  enters  the  pons 
on  its  ventral  surface,  in  line  -with  the  roots  of  the  seventh,  eighth, 
ninth,  tenth  and  accessory  nerves  (Fig.  85).  The  root  fibers  divide 
T-like;  the  short  ascending  branches  end  in  the  pontine  nucleus 
of  the  fifth  nerve  and  the  long  descending  branches,  forming  the 
spinal  tract,  terminate  in  the  nucleus  of  that  tract.  A  certain  few 
of  these  root-fibers  go  directly  to  the  motor  nucleus  of  the  trigemi- 
nal nerve  and  perhaps  to  other  motor  nuclei;  these  are  reflex  in 
function. 

From  the  trigeminal  nucleus  axones  establishing  reflex  and  cor- 
tical relations  run :  (a)  To  motor  nuclei  by  way  of  the  medial  long- 
itudinal bundle  and  directly  without  entering  that  bundle,  forming 
the  middle  link  of  reflex  arcs,  and  (b)  by  way  of  two  paths  they 
run  toward  the  cerebral  cortex  as  far  as  the  thalamus.  The  latter 
cross  the  median  raphe  and  probably  enter  the  medial  fillet  and 
the  spino-thalamic  tract.  The  axones  bearing  impulses  of  the 
muscular  sense  enter  the  medial  fillet  and  are  continued  through  it 
to  the  lateral  nucleus  of  the  thalamus;  those  fibers  which  conduct 
pain  and  temperature  impressions  run  through  the  spino-thalamic 
tract  to  the  same  nucleus.  Both  sets  of  fibers  conduct  tactile  im- 
pulses. From  the  thalamus  the  cortical  fillet  completes  the  path 
to  the  somaesthetic  cortex  of  the  cerebrum. 

Vestibular  Nuclei  {Nn.  Nervi  Vestibularis,  Figs.  92  and  93). — 
These  are  located  partly  in  the  pons  as  already  pointed  out,  and 
extend  as  low  as  the  mid-medulla.  Their  function  is  equiHbrium. 
The  principal  nucleus  (Schwalbe's)  is  dorso-medial  in  position 
and  lies  beneath  the  acustic  area  of  the  ventricular  floor,  crossed 
by  the  medullary  striae.  It  extends  transversely  from  near  the 
eminentia  medialis  almost  to  the  restiform  body.  It  appears 
to  receive  nearly  all  the  fibers  of  the  vestibular  nerv-e,  which  arbor- 


3o8  THE    RHOMBENCEPHALON. 

ize  and  terminate  about  its  cells.  Lateral  to  the  principal  nucleus 
are  the  nucleus  of  Deiters  and  the  nucleus  of  the  descending  root. 
Deiters's  nucleus  is  spread  along  the  medial  surface  of  the  resti- 
form  body,  chiefly  in  the  pons.  It  becomes  a  distinct  nucleus 
as  the  lower  border  of  the  pons  is  approached  and  grows  larger 
for  some  distance  above  that  point.  In  the  pons  it  is  bent  back- 
ward with  the  restiform  body  toward  the  cerebellum.  Its  upper 
end  is  thus  placed  in  the  lateral  wall  of  the  fourth  ventricle  between 
the  restiform  body  and  the  brachium  conjunctivum.  This  por- 
tion is  called  the  superior  nucleus  (of  Bechterew  or  Flechsig). 
Deiters's  nucleus  is  made  up  of  cell-bodies  which  are  large  in 
comparison  with  those  of  the  principal  nucleus.  It  receives  the 
descending  fibers  of  the  acustico-cerebellar  tract  from  cerebellar 
ganglia  and  cortex  and  originates  axones  that  proceed  down  the 
cord  in  the  anterior  descending  cerebello-spinal  tract,  thus  form- 
ing a  relay  in  the  cerebello-spinal  path;  and  this  is  its  chief  func- 
tion. It  is  only  a  subordinate  terminal  nucleus  of  the  vestibular 
nerve.  The  nucleus  of  the  descending  root  is,  in  all  probability, 
a  relay  station  in  the  conduction  path  from  the  vestibular  nerve, 
but  not  a  terminal  nucleus  of  that  nerve.  It  is  composed  of 
cell-bodies  scattered  through  a  strand  of  fibers,  called  the  descend- 
ing root,  which  extends  from  the  level  of  the  principal  nucleus 
down  to  the  nucleus  funiculi  cuneati  (Bruce).  It  is  placed  some- 
what under  cover  of  the  medial  border  of  the  restiform  body  and, 
with  the  enveloping  descending  root,  separates  this  body  from 
the  principal  nucleus.  Certain  fibers  of  the  descending  root 
terminate  in  the  nucleus  of  the  same  name. 

Cortical  Connections. — Axones  of  the  terminal  nuclei  of  the 
vestibular  nerve  enter  the  opposite  medial  fillet  and,  by  way  of  the 
descending  root,  also  the  nucleus  funiculi  cuneati.  The  medial 
fillet  continues  the  direct  path  to  the  thalamus  and  the  cortical 
fillet  completes  it  up  to  the  temporal  cortex.  The  descending 
root  and  the  arcuate  fibers  from  the  nucleus  funiculi  cuneati 
constitute  the  connecting  link  between  the  vestibular  nuclei  and 
the  cortex  of  the  cerebellum.  The  reflex  connections  of  the 
vestibular  nerve  are  established,  first,  with  cerebral  nerves,  by 
fibers  which  join  the  medial  longitudinal  bundle  and  terminate 


GRAY   MATTER    OF    MEDULLA.  309 

in  the  nuclei  of  motor  nerves;  second,  with  spinal  nerves  by  the 
axones  of  Purkinje's  cells  to  the  nucleus  fastigii  and  nucleus  glo- 
bosus;  from  the  cerebellar  ganglia  by  the  acustico-cercbellar 
tract  to  the  nucleus  of  Deiters,  and  then  by  way  of  the  anterior 
descending  cerebello-spinal  tract  to  the  motor  nuclei  of  the  spinal 
nerves  in  the  anterior  columna. 

Cochlear  Nuclei  (Nn.  Nervi  Cochlearis,  Fig.  92). — -There  are 
two  cochlear  nuclei,  the  ventral  and  the  lateral.  They  concern 
hearing  proper.  The  ventral  cochlear  nucleus  appears  in  section 
as  a  triangular  mass  of  cell-bodies  imbedded  in  the  medulla  at 
the  upper  end  of  the  posterior  lateral  sulcus.  It  lies  between  the 
restiform  body  and  the  olive;  the  vestibular  root  of  the  auditory 
nerve  separates  it  from  the  olive.  It  receives  the  greater  number 
of  fibers  in  the  cochlear  nerve  and  gives  rise  to  those  of  the  trap- 
ezoid body  and,  through  that,  to  a  large  part  of  the  lateral  fillet 
of  the  opposite  side ;  a  few  of  its  fibers  enter  the  fillet  of  the  same 
side.  In  the  corpus  trapezoideum,  the  cochlear  tract  is  largely 
relayed  by  the  neurones  forming  the  nuclei  of  the  superior  olivary 
group.  The  lateral  cochlear  nucleus  embraces  the  outer  surface 
of  the  restiform  body.  It  is  situated  both  lateral  and  dorsal  to 
the  ventral  nucleus  and,  stretching  around  the  posterior  surface 
of  the  restiform  body,  it  produces  the  ventricular  eminence  in 
the  lateral  part  of  the  acustic  area,  called  the  tuberculum  acusticum. 
The  lateral  nucleus  receives  that  part  of  the  cochlear  root  which 
does  not  end  in  the  ventral  nucleus,  and  the  fibers  arborize  about 
its  cells.  The  axones  of  the  lateral  nucleus  form  the  medullary 
striae;  a  few  of  them  enter  the  trapezoid  body  (Figs.  86,  89  and  92). 
The  medullary  striae  run  somewhat  obliquely  across  the  ventric- 
ular floor  to  the  median  groove,  plunge  forward  to  the  superior 
olivary  nuclei  of  the  opposite  side  where  they  are  partially  relayed 
and  then,  bending  upward,  are  continued  in  the  lateral  fillet. 
At  the  superior  oHvary  nuclei  of  the  opposite  side  the  fibers  from 
the  lateral  and  ventral  nuclei  become  intermingled,  hence  the 
trapezoid  body  and  medullary  striae  combine  in  the  formation  of 
the  lateral  -fillet.  The  lateral  fillet  sulTers  a  partial  relay  in  its 
o^^•n  nucleus,  after  which  it  separates  into  two  parts;  the  prin- 
cipal part  runs  to  the  internal  geniculate  body,  by  way  of  the 


310  THE   RHOMBENCEPHALON. 

brachium  inferius;  the  smaller  part  ends  in  the  quadrigeminal 
colliculi,  chiefly  in  the  inferior  colliculus  on  the  same  side.  From 
the  medial  geniculate  body  to  the  transverse  and  superior  temporal 
gyri,  the  acustic  path  is  formed  by  the  temporo-thalamic  (acustic) 
radiation.  This  completes  the  cortical  connection  of  the  cochlear 
nuclei.  Their  reflex  connections  are  established,  first,  by  the 
oHvary  pedicle  and  medial  longitudinal  bundle  and,  second,  by 
that  part  of  the  lateral  fillet  which  ends  in  the  colliculi  of  the 
corpora  quadrigemina  (see  pages  i6o  and  i6i). 

(3)  There  are  Certain  Special  Nuclei  of  the  Medulla. — 
These  are  not  represented  either  in  the  pons,  above,  or  the  spinal 
cord,  below.  They  are  the  nucleus  funiculi  gracilis,  the  nucleus 
funiculi  cuneati  and  the  nucleus  olivaris  inferior. 

Nucleus  Funiculi  Gracilis  and  Nucleus  Funiculi  Cuneati  (Figs. 
94  and  95). — ^The  nucleus  funiculi  gracilis  and  nucleus  funiculi 
cuneati  are  large  nuclei,  extending  from  the  level  of  the  olive  to 
the  lower  end  of  the  medulla.  They  are  situated  near  the  pos- 
terior surface  beneath  the  gracile  and  cuneate  funiculi,  whose 
fibers  terminate  in  them;  they  give  origin  to  the  medial  fillet,  and 
the  anterior  and  posterior  external  arcuate  fibers,  and  they  pro- 
duce, respectively,  the  clava  and  cuneate  tubercle  on  the  posterior 
surface  of  the  medulla.  In  successive  sections  from  below  upward, 
the  nucleus  funiculi  gracilis  is  first  seen  as  an  isolated  mass  of 
gray  substance  imbedded  in  the  funiculus  gracilis  at  the  level  of 
the  pyramidal  decussation.  It  enlarges  dorso-ventrally  and 
transversely  toward  its  upper  end,  as  is  shown  in  consecutive  sec- 
tions, and  reaches  its  greatest  size  at  the  clava,  where  it  receives 
the  terminal  end-tufts  of  the  funiculus  gracihs.  At  the  level 
of  the  clava  the  ventral  border  of  the  nucleus  funiculi  gracilis 
fuses  with  the  gray  matter  about  the  central  canal.  The  axones 
of  this  nucleus  form  about  one-half  of  the  medial  fillet  and  the 
external  arcuate  fibers.  The  nucleus  funiculi  cuneati  (Fig.  95) 
appears  at  the  same  inferior  level  as  the  nucleus  funiculi  gracilis. 
It  is  from  the  first  and  throughout  its  length  continuous  with  the 
central  gray  substance  on  which  it  appears  as  a  bud-like  outgrowth 
in  the  lower  medulla.  It  gradually  broadens  and  elongates  dorsal- 
ward  when  traced  upward  (Fig.  94).     Beneath  the  cuneate  tubercle 


GRAY   MATTER    OF   MEDULLA. 


311 


it  reaches  its-  full  stature  and  gathers  into  itself  the  fibers  of  the 
funiculus  cuneatus  and  the  descending  root  of  the  vestibular  nerve; 
thence  it  sends  its  own  axones  upward  in  the  medial  fillet  and  the 
external  arcuate  fibers.  Near  the  lower  end  of  the  medulla  there 
is  a  small  lateral  bud  of  gray  matter  connected  with  the  nucleus 
funiculi  cuneati,  to  which  it  is  accessory  and,  hke  it,  is  imbedded 
in  the  funiculus  cuneatus.  It  occupies  the  position  of  the  dorsal 
nucleus  (Clarki)  in  the  spinal  cord,  and  is  called  the  accessory 
nucleus  funiculi  cuneati. 

The  nuclei  funiculi  gracilis  et  cuneati  form  the  first  relay  station 
in  the  spino-cerebral  path  for  impressions  of  the  muscular  and 


Funiculus  gracilis 
Funiculus  cuneatus 


Nucleus  funiculi  gracilis 

Nucleus  funiculi  cuneati 


Tractus  spinalis 

n.  trigemini 


(Post.)  Cerebello  spinal 
tract 


Ant.  cerebello-spinal, 
spino-thalamic,    rubro-spinal 
triangular  tracts 


Nucleus  tractus  spinalis 
n.  trigemini 


Pyramid 


'/^     Head  of  ant.  columna 


Medial  and  anterior    \  Fasciculus 
longitudinal     bundles  J  proprius 
Pyramidal  decussation 


Fig-  95-— Section  of  the  medulla  oblongata  at  the  pyramidal  decussation. 
{Original.) 


tactile  senses,  and  lesions  in  them  cause  ataxia.  They  also  he 
at  the  dividing  of  the  ways;  the  direct  path  continuing  through 
the  fillet  decussation  and  the  medial  fillet  to  the  thalamus,  and 
the  indirect  path  running  through  the  arcuate  fibers  to  the  cere- 
bellar cortex.  From  the  cerebellar  cortex  the  impulses  proceed 
cerebralward  through  Purkinje's  neurones  to  the  dentate  nucleus 


312  THE    RHOMBENCEPHALON. 

and,  thence,  through  the  dentate  neurones  by  way  of  the  brachium 
conjunctivum  cerebeUi  to  the  opposite  red  nucleus  and  thalamus. 
The  cortical  fillet  conducts  all  common  sensory  impulses  from 
the  thalamus  to  the  cerebral  cortex. 

The  nucleus  olivaris  inferior,  the  oHvary  nucleus  of  the  medulla 
(Figs.  92  and  94),  is  a  sinuous,  pouch-like  collection  of  gray  matter  re- 
sembling the  nucleus  dentatus  of  the  cerebellum.  It  is  situated 
near  the  lateral  surface  of  the  medulla  and  is  invested  superficially 
and  deeply  by  fibers  from  the  lateral  fasciculus  proprius.  Its  open 
hilus looks  mediaWy  SLud  is  filled  with  fibers,  the  cerebello-olivary  fibers, 
which  join  it  to  the  opposite  hemisphere  of  the  cerebellum.  On 
either  side  of  the  oHvary  nucleus  is  an  accessory  nucleus — the 
medial  accessory,  in  the  anterior  area  among  the  fibers  of  the 
interoUvary  part  of  the  medial  fillet,  and  the  dorsal  accessory  in 
the  lateral  area.  The  oHvary  nucleus,  covered  by  fibers  of  the 
lateral  fasciculus  proprius,  forms  the  olive  (oliva).  The  olive 
shows  the  longitudinal  extent  of  the  nucleus  and  on  section  it  is 
seen  to  measure  a  quarter  of  an  inch  in  depth.  The  olivary  nucleus 
is  said  to  be  a  modern  structure;  it  is  found  well  developed  only 
in  the  higher  mammals  and  does  not  appear  in  the  human  brain 
until  the  sixth  month.  It  probably  contains  both  ascending  and 
descending  neurones.  Axones  enter  it  from  the  nucleus  funiculi 
gracilis  and  nucleus  funiculi  cuneati  and  probably  some  of  the 
cerebello-olivary  fibers  are  ascending  in  direction.  It  receives 
two  groups  of  descending  fibers,  viz.:  (a)  The  descending  cere- 
bello-olivary fibers  pass  down  from  the  cortex  of  the  cerebellum 
through  the  restiform  body  to  the  medulla,  decussate  and,  entering 
the  hilus  of  the  opposite  nucleus,  arborize  and  end  about  its  cell- 
bodies;  and  (b)  the  olivary  fasciculus  (central  tract  of  the  teg- 
mentum), having  descended  from  the  lentiform  nucleus  through 
the  mid-brain  and  pons,  fades  away  just  dorsal  to  the  olive  and 
probably  ends  in  it.  Axones  of  the  olivary  nuclei  of  the  medulla 
have  been  traced  by  Kolliker  and  others  down  the  lateral  column 
of  the  spinal  cord.  The  triangular  tract  of  Helwig  is  probably 
composed  of  such  fibers.  It  descends  along  the  surface  of  the 
cord  lateral  to  the  anterior  roots  of  the  spinal  nerves  and  ends 
in  the  gray  matter  of  the  cord. 


THE    FOURTH    VENTRICLE.  313 

Lesions  in  the  medulla  are  very  fatal  and  death  usually  occurs 
before  any  sensory  or  motor  phenomena  can  be  observed;  but 
rarely  the  pyramidal  tracts  alone  have  been  involved  or  the  pyram- 
idal tracts  together  with  one  or  more  of  the  roots  of  the  ninth  to 
the  twelfth  cerebral  nerves.  In  the  last  case,  crossed  paralysis 
is  produced,  as  in  the  pons,  affecting  the  cerebral  nerves  on  the 
same  side  and  the  opposite  spinal  nerves.  In  progressive  bulbar 
paralysis  the  motor  nuclei  of  the  medulla  are  involved  as  a  pre- 
liminary to  the  degeneration  of  the  anterior  gray  columna  in  the 
spinal  cord. 

RHOMBENCEPHALON. 
SECTION  IV.     THE  FOURTH  VENTRICLE. 

The  common  cavity  of  the  rhombencephalon  is  the  fourth 
ventricle  (veniriculus  quartus)  (Fig.  ii8).  The  fourth  ventricle 
is  contained  chiefly  in  the  pons  and  medulla,  and  is  ventral  to  the 
cerebellum  (Fig.  79).  It  is  broadest  at  the  junction  of  the  pons 
and  medulla  (Figs.  86  and  91).  Above  and  below^  that  junction, 
it  gradually  contracts  to  the  size  of  the  cerebral  aqueduct  and 
central  canal  of  the  spinal  cord,  ^vith  which  it  is  continuous. 
Infeiiorly  it  communicates  through  its  roof  with  the  subarachnoid 
space  via  three  apertures,  a  median  and  two  lateral.  The 
fourth  ventricle  is  a  gable-roofed  chamber  \Adth  a  diamond-shaped 
floor.  The  gables  (Fig,  79)  are  directed  lateralward  and  are 
prolonged  in  tunnel-like  extensions  around  the  restiform  body. 
The  long  axis  of  the  ventricular  floor  (Figs.  86  and  96)  is  parallel 
with  the  spinal  cord,  and  extends  from  the  superior  extremity  of 
the  pons  to  the  middle  of  the  medulla.  The  transverse  axis 
coincides  with  the  junction  of  the  pons  and  medulla.  Thus  the 
superior  triangle  of  the  floor  is  formed  by  the  pons;  the  inferior, 
by  the  medulla  oblongata.  The  fourth  ventricle  is  lined  vdih 
ependyma,  which  is  complete  throughout,  except  in  the  roof  of 
the  inferior  part,  where  below  the  inferior  medullary  velum  only 
the  epithelial  layer  is  present. 

Boundaries. — ^Thc  fioor  is  formed  by  the  pons  and  medulla. 


314  THE   RHOMBENCEPHALON. 

The  lateral  wall  (superior  triangle)  is  formed  by  the  brachium 
conjunctivum  of  the  cerebellum;  and  (inferior  triangle)  by  the 
taenia  of  the  fourth  ventricle  winding  across  the  restiform  body, 
funiculus  cuneatus  and  funiculus  gracilis  to  the  obex.  The  roof 
is  formed  by  the  superior  medullary  velum  (valve  of  Vieussens) 
superiorly;  and  by  the  inferior  medullary  velum  and  roof  epithe- 
lium, inferiorly  (Fig.  91).  The  superior  and  inferior  halves  of 
the  roof  meet  at  an  acute  angle,  the  fastigium,  and  form  the  tent 
of  the  fourth  ventricle  (Fig.  79).  On  either  side,  the  gable  is 
pushed  out  over  the  restiform  body  and  thus  is  formed  the  lateral 
recess.  The  lateral  recess  is  a  tunnel-hke  extension  of  the  ventric- 
ular cavity,  reaching  almost  to  the  posterior  lateral  sulcus.  The 
recess  is  bounded,  superiorly  and  ventrally,  by  the  restiform  body; 
dorsally,  by  the  inferior  medullary  velum;  and  inferiorly,  by  the 
roof  epithelium.  The  chorioid  plexuses  of  the  fourth  ventricle 
invaginate  the  roof  epitheHum  and  hang  from  the  roof  into  the 
lateral  recesses  and  the  inferior  part  of  the  cavity  (Fig.  91). 

Floor  of  the  Fourth  Ventricle.  {Fossa,  rhomboidea).—Be- 
cause  it  contains  the  nuclei  of  one  or  more  roots  of  the  posterior 
eight  (fifth  to  twelfth)  cerebral  nerves,  the  floor  of  the  fourth  ven- 
tricle' is  a  very  important  area  (Figs.  86  and  96).  A  median  groove 
bounded  by  the  eminentise  mediales  forms  the  long  axis  of  the 
diamond-shaped  floor  and  divides  it  into  two  lateral  halves;  the 
lateral  halves  are  bisected  transversely  by  a  number  of  lines,  the 
medullary  striae  (striae  medullares).  The  striae  are  produced  by 
bundles  of  fibers  which  rise  from  the  cochlear  nucleus  of  the 
auditory  nerve.  Diverging  somewhat  and  plunging  into  the 
medulla  at  the  median  groove,  the  fibers  of  the' striae  enter  the 
opposite  trapezoid  body  and  lateral  fillet.  The  medullary  striee 
divide  each  lateral  half  of  the  floor  into  a  superior  and  an  inferior 
triangle. 

Description  to  Fig.  96. 

a.  Nucleus  of  olfactory  nerves,  b.  Nucleus  of  oculomotor  nerve,  c.  Nucleus  of  trochlear 
nerve,  d.  Nucleus  of  descending  root  of  trigeminus,  e.  Chief  motor  nucleus  of  trigeminus. 
f.  Nucleus  of  facial,  g.  Nucleus  of  abducens.  h.  Nucleus  ambiguus  (vagus  and  glosso- 
pharyngeus).  i.  Nucleus  of  ihypoglossus.  j.  Nucleus  of  accessory  nerve.  Nuclei  of  optic 
nerve:  k.  Pulvinar  of  thalamus,  1.  Lateral  geniculate  body,  m.  Nucleus  of  superior  coUicu- 
lus.  n.  Sensory  nucleus  of  trigeminus,  o.  Nucleus  of  vestibular  nerve,  p.  Ventral  nucleus 
of  cochlear  nerve,  q.  Lateral  nucleus  of  cochlear  nerve,  r.  Nucleus  alae  cinereas  (vagus  and 
glossopharyngeus) .  s.  Solitary  tract  (vagus  and  glossopharyngeus) .  t.  Nucleus  of  spinal 
tract  of  trigeminus. 


THE    FOURTH    VENTRICLE. 


315 


I'ig.  96. — Nuclei  of  the  cerebral  nerves  in  the  medulla,  pons,  mid-brain,  inter-brain 
and  olfactory  bulb.  Motor  (or  genetic)  nuclei,  red;  terminal  (or  sensory) 
nuclei,  blue.     (After  Morris's  Anatomy.) 


THE    FOURTH    VENTRICLE.  317 

The  superior  triangle  of  the  floor  presents  the  colliculus 
faciahs,  superior  fovea,  locus  ca.'ruleus  and  a  part  of  the  acustic 
area. 

The  colliculus  facialis  (Fig.  86),  the  superior  extremity  of 
the  eminentia  mediahs,  is  located  next  the  median  groove.  It  is 
produced  largely  by  the  genu  of  the  facial  nerve.  Beneath  it  is 
the  nucleus  of  the  abducent  (sixth)  nerve  (Fig.  96).  External  to 
it  and  in  front  of  the  stride  medullares  is  a  small  fossa,  the  fovea 
superior. 

Fovea  Superior  (Fig.  86). — ^The  fovea  superior  is  near  the  lateral 
wall  of  the  ventricle  and  marks  the  location  of  the  facial  nucleus 
(seventh)  and  the  salivary  nucleus  of  the  intermediate  nerve, 
which  are  deeply  seated  in  the  pons.  Running  upward  along 
the  wall  of  the  ventricle  from  the  superior  fovea,  is  the  sulcus 
limitans.  It  is  a  blue-floored  groove  in  the  pons,  called  locus 
Cceruleus. 

The  locus  cceruleus  (Fig.  86)  continues  to  the  superior  angle 
of  the  ventricle.  The  blue  color  is  due  to  the  substantia  ferrugi- 
nea,  a  pigmented  layer  of  cell-bodies  underlying  the  ependyma. 
The  principle  motor  nucleus  of  the  trigeminal  nerve  (fifth)  hes 
beneath  the  superior  part  of  the  locus  casruleus  (Fig.  96). 

Inferior  Triangle  of  the  Ventricular  Floor. — It  presents: 
The  trigonum  hypoglossi,  fovea  inferior,  ala  cinerea  and  eminentia 
cinerea,  and  most  of  the  area  acustica  (Fig.  86). 

The  hypoglossal  triangle  (Fig.  86)  is  produced  by  the  inferior 
half  of  the  eminentia  medialis.  Its  apex  is  in  the  inferior  angle 
of  the  ventricle,  and  forms  one  nib  of  the  calamus  scriptorius; 
its  base  looks  upward  and  is  situated  under  the  medullary  strife. 
The  twelfth  nerve  rises  from  the  column  of  cells  whose  upper  one- 
half  is  covered  by  it  (Fig.  96).  External  to  the  trigonum  hypo- 
glossi and  inferior  to  the  strige  medullares  is  the  inferior  fovea, 
which  forms  the  apex  of  the  ala  cinerea. 

Ala  Cinerea  {Trigonum  Vagi,  Fig.  86). — ^The  vagus  triangle 
is  of  a  darker  color  than  the  ventricular  floor  around  it,  hence  the 
name,  ala  cinerea.  The  inferior  fovea  forms  the  depressed  and 
superiorly  directed  apex  of  the  ala;  its  floor  rises  interiorly  to  the 
base,  eminentia  cinerea,  which  is  directed  toward  the  clava.     The 


3l8  THE    RHOMBENCEPHALON. 

nucleus  alse  cinereae,  the  nucleus  tractus  solitarii  and  the  nu- 
cleus ambiguus,  three  nearly  parallel  columns  of  cell-bodies  a  half- 
inch  in  length,  are  in  part  covered  by  the  ala  cinerea  (Fig.  96). 

The  superior  and  inferior  fovese  and  the  sulcus  limitans  fossae 
rhomboideas  in  which  they  are  located  represent  the  lateral  sul- 
cus, which  in  the  embryo  separates  the  ventral  from  the  dorsal  zone 
of  the  rhombencephalon. 

Area  Postrema. — ^Below  the  ala  cinerea  and  between  it  and  the 
taenia  ventriculi  quarti,  there  is  a  small  fusiform  strip  of  the  ven- 
tricular floor  which  Retzius  has  called  the  area  postrema.  An 
oblique  stria  separates  it  from  the  base  of  the  ala  cinerea. 

The  area  acustica  occupies  the  lateral  angle  of  the  ventricular 
floor  (Fig.  86).  It  is  partly  in  the  superior  triangle,  but  chiefly 
in  the  inferior.  Inclosed  between  the  ala  cinerea  and  the  taenia, 
its  apex  points  downward,  and  its  base  looks  upward  and  is  crossed 
by  the  medullary  striae.  A  slight  eminence,  the  tuberculum 
acusticum,  makes  the  lateral  angle  of  the  acustic  area  most  prom- 
inent. Beneath  the  acustic  area  are  the  vestibular  nuclei  of  the 
auditory  nerve ;  also  the  lateral  part  of  the  cochlear  nucleus,  which 
is  found  ill  the  acustic  tubercle  (Fig.  96). 

ORIGIN  OF  CEREBRAL  NERVES. 

According  to  Sommering,  there  are  twelve  pairs  of  cerebral 
nerves  (nervi  cereb rales),  but  to  this  must  be  added  the  nervus 
intermedius  (pars  intermedia)  which,  though  associated  with 
the  facial  nerve  in  the  facial  canal,  is  of  itself  a  true  mixed  nerve. 
The  first,  second  and  eighth  cerebral  nerves  are  purely  sensory; 
six  of  them,  the  third,  fourth,  sixth,  seventh,  eleventh  and  twelfth, 
are  purely  motor;  while  the  fifth,  the  intermediate,  the  ninth  and 
tenth  are  mixed  nerves  and  contain  both  efferent  and  afferent 
fibers. 

Cerebral  Nerves,  Nervi  Cerebrales  (Figs.  86  and  96). — 

1.  Olfactory  (nn.  olfactorii) — special  sense  of  smell. 

2.  Optic    (n.    opticus) — special   sense    of    sight. 

3.  Oculomotor  (n.  oculomotorius) — ^motor. 

4.  Trochlear  (n.  trochlearis) — motor. 


ORIGIN    OF    CEREBRAL    NERVES.  319 

5.  Trigeminal   (n.  trigeminus) — motor   and    common  senson-. 

6.  Abducent  (n.  abducens) — motor. 

7.  Facial  (n.  facialis) — motor. 

Intermediate     (n.     intermedius) — special     sense    of    taste, 
secretory  and  trophic. 

8.  Acustic  (n.  acusticus) — special  senses  of  hearing  and  equi- 

librium. 

9.  Glossopharyngeal  (n.  glossopharyngeus) — Special   sense  of 

taste,  common  sensory,  secretory,  trophic  and  motor. 

10.  Vagus  (n.  vagus) — motor,  vaso-motor,  viscero-motor,  inhibi- 

tory, secretory,  trophic  and  common  sensor}^ 

11.  Accessory  (n.  accessorius) — motor. 

12.  Hypoglossal  (n.  hypoglossus) — motor. 

All  cerebral  nerves  are  connected  with  the  brain  and,  when  their 
functions  were  not  understood,  these  points  of  connection  were 
indiscriminately  called  origins;  but  with  our  present  knowledge 
of  the  functions  and  development  of  the  pure  sensory  and  the 
mixed  nerves  such  use  of  the  term  "origin"  is  not  admissible. 
Pure  sensory  nerves  and  the  sensory  roots  of  mixed  nerves  take 
their  origins  from  ganglia  situated  wholly  outside  the  brain.  From 
those  gangha  the  dendrites  grow  outward  to  the  peripheral  dis- 
tribution of  the  respective  nerves;  the  axones  grow  centrally  into 
the  brain,  where  they  arborize  and  end  in  groups  of  cell-bodies 
forming  nuclei.  Such  ner\'es  conduct  impulses  from  the  per- 
iphery to  these  nuclei,  hence  the  name  applied  to  them  is  terminal 
nuclei  {nuclei  terminales).  See  the  blue  nuclei.  Fig.  96.  The 
motor  nerves  and  the  motor  roots  of  mixed  nerves  take  their 
origins  inside  the  brain  from  groups  of  cell-bodies  also  called 
nuclei.  The  axones  grow  outward  from  these  latter  nuclei  toward 
the  periphery;  they  conduct  impulses  from  the  nuclei  to  the  mus- 
cles or  to  the  secreting  cells  in  their  respective  areas  of  distribution, 
hence  the  nuclei  of  motor  nerves  and  motor  roots  are  genetic  nu- 
clei {nuclei  origines).  See  the  red  nuclei.  Fig.  96.  Thus  it  is  seen 
that  the  brain  coimection  of  a  motor  nerve  is  its  true  origin,  while 
this  connection  is  the  real  termination  of  a  sensory  nerve. 


320 


THE    RHOMBENCEPHALON. 


TABLE  II. 

SENSORY  NERVES  AND  SENSORY  ROOTS. 

Ganglion  of  Origin.      Entrance  Into  Brain.       Terminal  Nucleus. 


Olfactory  cells  in  nasal 
mucous  membrane. 


Ganglionar  layer  of  the 
retina. 


Mitral  and  brush  cells 
of  bulb  (a  part  of  cere- 
bral hemisphere). 

Nuclei  of  same  in  inter- 
brain  and  mid-brain. 


I.  Olfactory  {Smell). 
Under  surface  of  olfac- 
tory bulb. 

2.  Optic  (Sight). 
Surface  of  lateral  genic- 
ulate body,  pulvinar 
of  thalamus  and  su- 
perior quadrigeminal 
colliculus. 

5.  Trigeminal  {Sensory  Root). 

Anterior  surface  of  the     Nucleus  tractus  spinalis 
pons.  n.   trigemini   reaching 

from  mid-pons  to  sec- 
ond cervical  nerve. 

Intermediate  Nerve  {Sensory  Root)  {Taste). 
Geniculate  ganglion.  Groove    between    pons     Nucleus  tractus  solitarii 

and  medulla,  between        beneath  inferior  fovea 
seventh    and  eighth        in  medulla, 
nerves. 


Semilunar  ganglion. 


Cochlear  Root. 

ganglion  (of  Corti). 


8.  Acustic  {Hearing  and  Equilibrium). 
Spiral     Groove    between   pons     Cochlear  Nuclei. 
and  medulla. 


Vestibular  Root. — Vestib- 
ular ganglion. 


Ven- 
tral and  lateral,  placed 
ventral  and  lateral  to 
restiform  body  in  me- 
dulla. 
Vestibular  Nuclei.— Vrm- 
cipal,  Deiters's  and  nu- 
cleus  of  descending 
root,  in  floor  of  fourth 
ventricle  in  medulla. 

9.  Glossopharyngeal  {Sensory  Root)  {Taste,  etc.). 
Superior    and    petrosal     Posterior  lateral  sulcus     Nucleus  tractus  solitarii 
ganglia    in    jugular        of  medulla.  and  nucleus   alae   cin- 

foramen.  erese  in  medulla. 


ORIGIN    OF    CEREBRAL    NERVES.  32 1 

10.  Vagus  (Sensory  Root). 

Jugular   and   nodular    Posterior  lateral  sulcus     Nucleus  ala;  cinereae,  and 
ganglia   in   jugular        of  medulla.  perhaps  nucleus  tractus 

foramen  and  below  it.  solitarii,  in  medulla. 

TABLE  III. 
MOTOR  NERVES  AND  MOTOR  ROOTS. 
Genetic  Nucleus.  Apparent  Origin  (Exit  from  Brain). 

3.  Oculomotor  {Motor  Nerve). 

Nucleus  in  floor  of  cerebral  aqueduct       Interpeduncular  fossa  of  mid-brain, 
in  mid-brain  under  superior  collic- 
ulus. 

4.  Trochlear  (Motor  Nerve). 

Nucleus  in  floor  of  cerebral  aqueduct       Superior  medullary  velum  in  isthmus 
in  mid-brain  under  inferior  collie-  rhombencephali. 

ulus. 

5.  Trigeminal  (Motor  Root). 

Nucleus  in  floor  of  cerebral  aqueduct       Anterior  surface  of  pons, 
in  mid-brain  and  under  locus  caer- 
uleus  of  pons. 

6.  Abducent  (Motor  Nerve). 

Nucleus   under  coUiculus  facialis  in       Groove  between  pons  and  medulla, 
pons. 

7.   Facial  (Motor  Nerve). 
Nucleus  under  fovea  superior  in  pons.       Groove  between  pons  and  medulla. 

Intermediate  (Efferent  Part,  Secretory). 
Dorsal  part  of  facial  nucleus  in  pons.        Groove  between  pons  and  medulla. 

9.  Glossopharyngeal  (Motor  Root). 

Nucleus  alae  cinereae  and  nucleus  am-       Posterior  lateral  sulcus  of  medulla, 
biguus  in  the  medulla.  upper  end. 

10.   Vagus  (Motor  Root). 

Same   as  ninth,  but   chiefly  nucleus       Posterior  lateral  sulcus  below  ninth, 
ambiguus.  and  between  olive  and  restiform 

body. 


32  2  THE    RHOMBENCEPHALON. 

II.   Accessory  {Motor  Nerve). 

Cerebral  Root. — Nucleus  ambiguus  in  Posterior  lateral  sulcus  of  medulla 
closed  medulla.  below  level  of  olive. 

Spinal  Root. — Nucleus  in  lateral  part  Lateral  surface  of  cord  between  liga- 
of  base  of  anterior  columna — upper  mentum  denticulatum  and  poste- 

five  segments  of  cord.  rior  roots  of  spinal  nerves. 

12.   Hypoglossal  {Motor  Nerve). 
Nucleus  under  trigonum  hypoglossi,       Anterior  lateral  sulcus   of  medulla 
floor  of    fourth  ventricle,   and  in  between  pyramid  and  olive, 

closed  medulla. 

Terminal  Nuclei. — ^The  terminal  nuclei  of  the  first  and  second 
cerebral  nerves  are  peculiar  and  cannot  as  yet  be  classified  with 
the  nuclei  of  other  sensory  nerves  and  sensory  roots  (Figs.  26, 
43  and  63).  The  terminal  nuclei  of  the  fifth,  the  intermediate, 
the  eighth,  ninth  and  tenth  nerves  may  be  called  the  posterior 
columna  series;  because  they  are  formed  by  masses  of  cell-bodies 
representing  the  upward  prolongation  of  the  posterior  columna 
of  gray  substance  in  the  spinal  cord.  Terminal  nuclei  are  com- 
mon sensory  and  special  sensory. 

Common  Sensory  Nuclei  (Fig.  96). — Of  the  posterior  columna 
series  of  nuclei,  the  terminal  nucleus  of  the  fifth  and  of  the  tenth 
nerves  and  a  part  of  the  terminal  nucleus  of  the  ninth  nerve  receive 
common  sensory  impulses,  and  transmit  them  to  the  opposite  thala- 
mus by  two  routes,  viz.,  through  the  medial  fillet  and  through  the 
spino-thalamic  tract.  Impulses  of  the  muscular  sense  travel  over 
the  former  route ;  those  of  the  pain  and  temperature  senses,  over 
the  latter;  and  tactile  impressions  are  beheved  to  traverse  both 
routes  aUke.  From  the  thalamus  these  impulses  are  carried  to 
the  cortex  of  the  posterior  central  gyrus.  Thus  is  the  cortical 
connection  of  these  nuclei  estabhshed;  and  each  is  brought  into 
refiex  connection  with  motor  nuclei  by  axones  of  the  terminal 
nuclei  which  run  chiefly  through  the  medial  longitudinal  bundle 
and  terminate  in  the  motor  nuclei. 

Special  Sense  Nuclei. — ^The  cortical  connection  of  the  nucleus 
tractus  solitarii,  which  receives  taste  impulses  from  the  glosso- 
pharyngeal and  intermediate  nerves,  has  not  been  definitely  traced; 
but  it  is  probably  relayed  in  the  thalamus  and  is  estabhshed  by 


ORIGIN    OF    CEREBRAL    NERVES.  323 

fibers  of  the  formatio  reticularis,  in  the  pons  and  mid-brain,  and, 
in  the  hemisphere,  by  certain  fibers  of  the  internal  capsule  which 
end  in  the  fusiform  gyrus  (?).  The  cochlear  nuclei  (ventral  and 
lateral)  receive  true  impulses  of  hearing  and  conduct  them  on  to- 
ward the  cerebral  cortex  by  w^ay  of  their  axones,  which  form  the 
trapezoid  body  and  medullary  striae  and  then  unite  in  forming 
the  lateral  fillet  (Fig.  89).  The  remaining  links  of  the  cortical 
connection  are  formed  by  the  brachium  inferius  and  the  acustic 
radiation  (radiatio  temporothalamica).  The  reflex  connection 
of  these  nuclei  is  somewhat  indirect.  It  is  established  in  part  by 
certain  fibers  of  the  lateral  fillet  which  end  in  the  quadrigeminal 
colHculi,  together  with  the  anterior  longitudinal  bundle;  but  is 
chiefly  brought  about  by  the  olivary  pedicle  and  the  me- 
dial longitudinal  bundle.  The  vestibular  nuclei — the  principal 
(Schwalbe's),  Deiters's  and  the  nucleus  of  the  descending  root — 
concern  equilibrium.  They  receive  impulses  from  the  vestibule 
and  semicircular  canals  of  the  internal  ear.  They  have  a  cerebral 
and  a  cerebellar  cortical  connection.  The  former  is  established 
as  far  as  the  thalamus,  by  the  opposite  medial  fillet,  and  com- 
pleted by  the  cortical  fillet;  and  the  latter  is  formed  by  the  de- 
scending root,  which  ends  in  the  nucleus  funiculi  cuneati,  and  the 
external  arcuate  fibers.  With  the  cerebral  motor  nerves,  these 
nuclei  are  brought  into  reflex  connection,  first,  by  axones  entering 
the  medial  longitudinal  bundle  and  terminating  in  the  motor 
nuclei;  and,  second,  probably  by  fibers  of  the  brachium  conjunc- 
tivum  which  become  connected  with  the  nuclei  of  the  third,  fourth 
and  sixth  cerebral  nerves.  The  reflex  connection  \vith  spinal 
nerves  is  formed  by  the  anterior  descending  cerebello-spinal  tract, 
viz.,  by  axones  of  Purkinje's  cells,  the  acustico-cerebellar  tract, 
the  cerebello-olivary  fibers  and  descending  fibers  from  Deiters's 
and  the  inferior  olivary  nuclei. 

The  terminal  nuclei  of  the  optic  nerve  are  situated  in  the  lateral 
geniculate  body,  the  pulvinar  of  the  thalamus  and  the  superior 
colhculus  of  the  corpora  quadrigemina  (Fig.  43).  Like  the  ter- 
minal nucleus  of  the  olfcictory  nerve,  these  cannot  at  present  be 
included  in  the  posterior  columna  series,  because  the  ventral  and 
dorsal  zones  of  the  embrj^onic  fore-brain  have  not  been  sufiiciently 


324  THE    RHOMBENCEPHALON. 

elucidated.  If  the  sulcus  hypothalamicus  really  separate  ventral 
from  dorsal  zone  in  the  inter-brain,  as  is  claimed  by  many,  it  would 
seem  that  both  the  optic  and  olfactory  terminal  nuclei  might  be 
included  in  the  posterior  series ;  but  there  is  need  of  further  inves- 
tigation, as  this  places  the  whole  cerebral  hemisphere  in  the  dor- 
sal zone. 

The  cortical  connection  of  the  terminal  nuclei  of  the  optic  nerve 
(Fig.  67)  is  established  by  fibers  of  the  optic  radiation  (radiatio 
occipito-thalamica)  which  rise  in  the  lateral  geniculate  body  and 
in  the  pulvinar  of  the  thalamus  and  terminate  in  the  cortex  of  the 
calcarine  region  of  the  occipital  lobe.  From  this  cortical  center, 
corticifugal  fibers  run  through  the  occipito-thalamic  radiation 
and  brachium  superius  to  the  superior  quadrigeminal  colliculus. 
This  colliculus  also  receives  a  few  fibers  directly  from  the  outer 
root  of  the  optic  tract;  it  thus  becomes  the  center  of  optic  reflexes; 
and  axones  of  the  superior  colliculus  form  the  anterior  longitudinal 
bundle,  which  completes  the  connection  with  opposite  motor  nuclei. 

The  terminal  nucleus  of  the  olfactory  nerve  is  situated  in  the  olfac- 
tory bulb  (Figs.  26  and  63).  The  axones  of  this  nucleus  establish 
direct  cortical  connection,  first,  -with  the  uncinate  region  and  an- 
terior perforated  substance  by  way  of  the  lateral  olfactory  stria 
and,  probably,  by  way  of  the  intermediate  stria;  and,  second,  with 
the  parolfactory  area,  the  olfactory  triangle,  the  gyrus  subcallosus 
and  the  gyrus  cinguli  through  the  fibers  of  the  medial  stria  of  the 
olfactory  tract.  The  reflex  connection  of  the  olfactory  nerve  is 
but  little  understood.  The  following  probabilities  may  be  stated : 
First,  the  fornix,  stria  medullaris  thalami,  fasciculus  retroflexus 
and  axones  of  interpeduncular  ganglion;  second,  the  fornix,  thala- 
mo-mammillary  bundle  and  descending  axones  of  the  thalamus; 
and,  third,  the  fornix  and  the  pedunculo-mammillary  bundles 
running  into  mid-brain,  pons  and  medulla. 

Genetic  Nuclei  (Nn.  Origines)  (Fig.  96). — The  nuclei  of  the 
oculomotor,  trochlear,  abducent,  facial,  accessory  and  hypoglos- 
sal nerves  and  the  nuclei  of  the  motor  roots  of  the  trigeminal, 
glossopharyngeal  and  vagus  nerves  represent  the  anterior  columna 
of  gray  matter  in  the  cord  and  constitute  the  anterior  columna 
series.     These  nuclei  are  connected  with  the  cerebral  cortex  on  both 


ORIGIN    OF    CEREBRAL    NERVES.  325 

sides,  but  chiefly  with  that  of  the  o])posite  hemisphere.  The  con- 
nection is  estabhshed  first  and  principally  by  the  pyramidal  tracts, 
some  of  the  fibers  running  directly  from  the  tract  to  the  nucleus, 
and  others,  leaving  the  tract  high  up,  run  through  the  accessory 
-fillet  (Bechterewi)  to  a  point  near  the  respective  nuclei  which  they 
are  about  to  enter;  and,  second,  the  fronto-pontal,  temporo- 
pontal  and  intermediate  tracts  are  believed  to  send  some  fibers  to 
the  genetic  nuclei  of  the  same  side.  The  reflex  connection  of  these 
genetic  nuclei  is  established  for  all  of  them  by  the  medial  long- 
itudinal bundle;  by  the  anterior  longitudinal  bundle  and  by  the 
olivary  pedicle  (for  the  third,  fourth,  and  sixth),  by  the  trape- 
zoid body  (for  the  seventh)  and  by  the  spinal  tract  of  the  tri- 
geminal nerve  (for  the  fifth,  seventh,  and  twelfth). 


CHAPTER  V. 

MEMBRANES  OF  THE  SPINAL  CORD. 

(MENINGES  SPINALIS.) 

Dura  Mater. — ^Through  the  foramen  magnum  the  membranes 
of  the  brain  are  continuous  with  those  of  the  cord  with  which  they 
are  very  similar  in  structure.  The  dura  mater  spinalis  is  attached 
to  the  margin  of  the  great  foramen  and  to  the  bodies  of  the  first 
two  or  three  cervical  vertebras;  elsewhere,  though  joined  to  the 
vertebrae  by  fibrous  bands,  its  surface  is  free  from  immediate  bony 
attachment  and  it  does  not  possess  the  periosteal  layer.  Thus 
suspended,  it  hangs  as  an  open  sack,  or  sheath  (Fig.  loo)  and 
reaches  down  to  the  third  sacral  vertebra,  where  it  is  constricted 
to  a  fibrous  cord  which  )3lends  with  the  periosteum  on  the  posterior 
surface  of  the  coccyx.  The  arachnoid  and  pia,  and  the  spinal 
cord  and  cauda  equina  are  contained  in  the  dural  sack  (Figs. 
97,  98  and  100). .  Externally,  the  surface  of  the  dura  is  separated 
from  the  wall  of  the  spinal  canal  by  the  internal  vertebral  plexus 
of  veins,  areolar  tissue  and  fat.  The  outer  surface  is  composed 
of  fiat  polygonal  cells,  like  the  inner  surface.  Its  internal,  serous 
surface  is  bathed  with  a  small  amount  of  cerebro- spinal  fluid  which 
separates  it  from  the  arachnoid.  For  every  segment  of  the  spinal 
cord,  the  dura  presents,  on  either  side,  a  pair  of  foramina,  through 
which  run  the  anterior  and  posterior  roots  of  the  spinal  nerves. 
(Fig.  97).  Those  nerve  roots  are  invested  by  a  sheath  of  dura 
prolonged  from  the  margins  of  the  foramina.  The  dura  mater 
of  the  cord  does  not  separate  into  two  layers,  and  forms  neither 
sinuses  nor  processes.  It  performs  no  periosteal  function  and 
possesses  no  arachnoid  granulations  (pacchionian  bodies).  Its 
two  surfaces  are  formed  by  endothelium. 

Arachnoid. — ^The  arachnoid  of  the  spinal  cord  (arachnoidea 
spinalis)  forms  a  sack  of  the  same  length  as  the  dural  sheath, 
with  which  it  is  externally  in  contact  (Figs.  97,  98  and  100).     It 

326 


MEMBRANES    OF    THE    SPINAL    CORD. 


327 


Septum  posticum 


Subarachnoid  trabecula 
with  bundles  of  poste- 
rior nerve-roots 

Ligamentum 
denticulatum 


Anterior  nerve-roots 
(jin  sections) 


Subarachnoid  space 


Dura  mater  — 


Ligamentum  denticulatum 


Linea  splendens' 


Arachnoid 


Posterior  root 
Anterior  root 


Dura  mater 


B 


Fig.   97. — Meninges  of  the  spinal  cord.      A.   Transverse  section.     (After  A>,v  and 
Retzius.)      B.  Anterior  view.     {Aftt'T  Ellis.     Morris's  Anatomy.) 


MEMBRANES    OF    THE    SPINAL    CORD. 


329 


presents  two  serous  surfaces.  Internally,  bands  of  fibro-elastic 
tissue  attach  it  to  the  pia  mater  along  the  posterior  median  line 
of  the  cord  and  form  the  subarachnoid  septum  (Fig.  97).  The 
external  spinal  veins  and  a  considerable  space  separate  the  arach- 
noid from  the  pia  mater.  That  subarachnoid  space  is  filled  with 
fluid.  By  the  ligamenia  denticulata  it  is  divided  into  the  anterior 
and  posterior  subarachnoid  spaces,  which,  through  the  foramen 
magnum,  are  continuous  with  the  same  spaces  in  the  cranial 
cavity  (Figs.  97  and  6). 

Pia  Mater. — ^The  pia  of  the  cord  {pia  mater  spinalis)  is  much 
stronger  than  that  of  the  brain  (Figs.  97  and  98).     It  has  two 


Ligamentum  denticulatum 


Interverte- 
bral foramen 


Body  of 
vertebra 
Periosteum 

Dura  mater 

Subdural 

space 

Arachnoid 

Subarachnoid 

space 

Pia  mater 


Fig.  98. — Diagrammatic  section  of  the  spinal  meninges  and  spinal  cord. 
(After  Morris's  Anatomy.') 


distinct  layers,  the  inner  of  which  is  continuous  with  the  brain 
pia  and  forms  an  epineurium  for  the  cord  and  roots  of  the  spinal 
nerves.  The  outer  is  the  more  vascular  layer.  Both  layers  dip 
into  the  anterior  median  fissure;  they  form  the  anterior  septum 
which  contains  the  anterior  spinal  artery.  The  inner  layer  is 
attached  to  the  septum  in  the  posterior  median  fissure.  The  outer 
layer  forms  the  linea  splendens  along  the  front  of  the  cord,  and  the 


33°  MEMBRANES    OF    THE    SPINAL    CORD. 

ligamenium  denticulatum  on  either  side.  The  denticulate  liga- 
ment is  a  longitudinal  band  whose  smooth  medial  border  is  con- 
tinuous with  the  pia  along  the  middle  of  the  lateral  surface  of 
the  cord ;  its  lateral  border  is  notched  and  its  twenty  teeth,  invested 
with  arachnoid,  are  attached  to  the  dura  opposite  the  first  twenty 
vertebrae.  The  two  Ugaments  subdivide  the  space  between  the 
pia  and  arachnoid  into  anterior  and  posterior  subarachnoid  spaces. 
A  filamentous  extension  of  the  pia  below  the  cord  proper  helps 
to  form  the  -fHum  terminale  internum.  It  descends  in  the  arachno- 
dural  sheath  with  the  roots  of  the  lumbar  and  sacral  nerves,  and 
all  together  constitute  the  cauda  equina  (Fig.  loo).  For  some 
distance,  about  half  its  length,  the  filum  terminale  internum  con- 
tains gray  matter  and  rudimentary  fibers  continuous  with  the 
spinal  cord.  The  filum  unites  with  the  arachnoid  and  dura  at 
the  third  sacral  vertebra  in  forming  the  jilum  terminale  externum 
which  forms  a  sort  of  Hgament  for  the  spinal  cord.  That  liga- 
ment is  inserted  into  the  coccyx.  The  pia  mater  of  the  cord  con- 
tains the  trunks  and  large  branches  of  the  anterior  and  the  two 
posterior  spinal  arteries,  and  the  tributaries  of  the  external  spinal 
veins. 

Nerve  Supply. — ^The  membranes  of  the  spinal  cord  are  sup- 
pHed  by  recurrent  branches  of  the  spinal  nerves  and  by  the  sympa- 
thetic. The  recurrent  branches  are  sensory  in  function. 

BLOOD  SUPPLY  OF  THE  SPINAL  CORD. 

The  vessels  supplying  the  cord  are  the  anterior  spinal  artery 
and  the  two  posterior  spinal  arteries,  which  rise  at  the  foramen 
magnum  from  the  vertebral  arteries,  and  are  reinforced  by  cervical, 
intercostal  and  lumbar  arteries.  The  anterior  spinal  artery 
{a.  spinalis  anterior)  descends  along  the  entrance  to  the  anterior 
median  fissure  (Fig.  99) ;  it  is  formed  by  the  union  of  two  vessels, 
one  from  each  vertebral.  The  posterior  spinal  artery  {a.  spinalis 
posterior)  of  either  side,  is  in  reaHty  a  pair  of  vessels  which  freely 
communicate,  and  are  so  placed  as  to  embrace  the  posterior  nerve 
roots.  The  larger  vessel  of  the  pair  is  anterior  to  the  nerve  roots, 
while  the  smaller  is  between  them  and  the  posterior  median  fissure 


BLOOD    SUPPLY    OF    THE    SPINAL    CORD. 


33^ 


(Fig.  loo).  The  spinal  arteries  give  origin  to  two  sets  of  branches, 
namely,  the  fissural  or  cenlrijugal,  and,  the  centripetal  arteries. 
Both  sets  are  end-arteries  and  form  rich  longitudinal  plexuses, 
which  overlap  each  other  but  do  not  anastomose. 

The  fissural  or  centrifugal  arteries  rise,  iirst  and  chie-fiy, 
from  the  anterior  spinal  artery  (Fig.  loo).  These  enter  the 
anterior   median    fissure    and,    running   lateralward,    supply  the 


'   P 


•f^^g-  99- — The  arteries  and  veins  in  the  spinal  cord.     Diagrammatic. 
(After  Morris's  Anatomy.) 

a.  Dorsal  external  spinal  veins,  b.  Posterior  radicular  vein.  c.  Peripheral  venous  ple.xus. 
a.  Anterior  radicular  vein.  e.  Ventral  external  spinal  veins,  f.  Anterior  central  vein.  g.  Pos- 
terior central  artery  and  vein.  h.  Posterior  spinal  artery,  i.  Peripheral  arterial  plexus. 
J.  Posterior  radicular  artery,  k.  Intercostal  artery.  1.  Spinal  ramus,  m.  Anterior  radic- 
ular artery,     n.  Interior  spinal  vein.    o.  Anterior  central  artery,     p.  Anterior  spinal  artery . 


greater  part  of  the  gray  matter.  Second,  a  few  centrifugal  arteries 
rise  from  the  posterior  spinal  arteries.  Running  into  the  posterior 
fissure,  they  are  distributed  to  the  posterior  white  columns,  the 
posterior  commissure  and  to  the  nucleus  dorsalis  (Clarki). 

The  centripetal  arteries  rise  from  both  the  anterior  and 
posterior  spinal  arteries  (Fig.  loo).  They  enter  the  cord  at  right 
angles  to  the  surface,  and  supply  the  white  matter  and  the  periph- 


332  MEMBRANES    OF    THE    SPINAL    CORE. 

eral  parts  of  the  gray  substance,  including  the  tips  of  the  columnae. 
Those  branches  to  the  columnae  accompany  the  root-fibers. 

Veins. — ^The  veins  that  carry  the  blood  from  the  interior  of 
the  cord,  the  venae  spinales  internae,  are  the  fissural  veins,  which 
issue  from,  the  fissures,  the  root-veins,  which  accompany  the  ante- 
rior and  posterior  root-fibers  to  the  surface  of  the  cord,  and  a 
small  number  of  veins  that  issue  from  other  parts  of  the  surface 
of  the  spinal  cord.  All  unite  in  forming  the  external  spinal  plexus 
(venae  spinalis  externae)  spread  over  the  entire  surface  of  the 
cord  beneath  the  arachnoid  membrane.  According  to  Cunning- 
ham, the  plexus  includes  six  longitudinal  veins — anterior  and 
posterior  median  and,  on  either  side,  an  antero-lateral  and  a 
postero-lateral  vein  placed  just  behind  the  respective  nerve  roots. 
In  the  upper  cervical  region,  the  plexus  forms  two  or  three  small 
veins  which  empty  into  the  vertebral  or  inferior  cerebellar  veins; 
elsewhere,  by  a  branch  along  each  spinal  nerve,  the  plexus  com- 
municates with  the  internal  vertebral  plexus  (plexus  venosi 
vertebrales  interni)  outside  the  dura  mater,  and  is  drained  into 
the  vertebral,  intercostal,  lumbar  and  sacral  veins.  No  valves 
are  found  in  the  spinal  veins. 

Lymphatics. — ^Perivascular  and  perineural  spaces  carry  the 
lymph  from  the  spinal  cord.  There  are  no  lymphatic  vessels 
in  the  cord. 


CHAPTER  VL 
THE  SPINAL  CORD. 

The  spinal  cord  {medulla  spinalis)  is  developed  from  the  posterior 
part  of  the  neural  tube,  and  forms  the  corresponding  portion  of 
the  central  axis  of  the  nervous  system. 

Extent. — It  is  continuous  with  the  medulla  oblongata,  above; 
and,  in  the  adult,  reaches  to  the  lower  border  of  the  first  lumbar 
vertebra  (Fig.  loo).  Its  length  is  seventeen  to  eighteen  inches. 
In  a  very  slender  process,  the  filum  terminale  internum,  the  cord 
is  continued  beyond  the  first  lumbar  vertebra.  That  process 
and  the  lower  spinal  nerves  form  the  cauda  equina,  which  is  in- 
closed in  a  sheath  composed  of  the  arachnoid  and  dura  mater. 
The  filum  terminale  internum  for  about  three  inches  contains  a 
prolongation  of  the  central  gray  matter  and  ventricle  of  the  cord; 
and,  also,  a  few  fibers,  which  suggest  the  coccygeal  ners-es  of  lower 
animals. 

In  the  foetus  before  the  third  month,  the  cord  and  spinal  canal 
are  of  equal  length.  At  birth  the  cord  reaches  the  third  lumbar 
vertebra,  and  it  continues  to  recede  with  the  rapid  growth  of 
the  vertebrae  to  adult  life. 

Diameters  (Fig.  loi). — ^The  spinal  cord  is  shaped  hke  a  cylin- 
der, slightly  flattened  from  before  backward  (dorso-ventrally).  Its 
longest  diameter  is  transverse  and  measures  less  than  half  an  inch, 
except  in  the  cervical  and  lumbar  enlargements  of  the  cord. 
In  the  latter,  it  equals  a  half-inch;  and,  in  the  former,  it  sHghtly 
exceeds  it.  The  thoracic  portion  of  the  cord  is  small  and  nearly 
cylindrical  in  shape.  Divested  of  its  meninges  and  nerves  the 
spinal  cord  weighs  about  one  ounce  and  a  half,  avoirdupois. 

The  cervical  enlargement  {intumescentia  cervicalis)  extends 
from  the  medulla  oblongata  to  the  second  thoracic  vertebra 
(Figs.  loo  and  loi).  Its  greatest  diameter  is  on  a  level  ^^ith  the 
fifth  intervertebral  disk.     It  gives  origin  to  the  motor  fibers  and 

Z2,2> 


334 


THE    SPINAL    CORD. 


receives  the  sensory  fibers  of  the  nerves  which  form  the  cervical 
and  brachial  plexuses. 

The  lumbar  enlargement  {intumescentia  lumhalis)  begins  at 
the  tenth  thoracic  vertebra  and  increases  to  the  twelfth  (Figs. 
loo  and  loi).     Opposite  the  first  lumbar  vertebra,  it  tapers  off 


Superior  or  Cervical  Segment    Middle  or  Dorsal  Portion     Inferior  Portion  of  Cord  and 
of  Spinal  Cord.  of  Cord.  Cauda  Equina. 

Fig.   loo. — Posterior  view  of  the  spinal  cord,  the  dura  mater  and  the  arachnoid 
being  laid  open  and  turned  aside.     (Brubaker  after  Sappey.) 

1.  Floor  of  fourth  ventricle.  2.  Brachium  conjunctivum.  3.  Brachium  pontis.  4.  Res- 
tiform  body.  5.  Clava.  6.  Glossopharyngeal  nerve.  7.  Vagus.  8.  Accessory  nerve.  9,  9,  9,  9. 
Ligamentum  denticulatum.  10,  10,  10,  10.  Posterior  roots  of  spinal  nerves.  11,  11,  11,  n. 
Posterior  lateral  sulcus.  12,  12,  12,  12.  Spinal  ganglia.  13,  13.  Anterior  roots  of  spinal 
nerves.  14.  Anterior  and  posterior  divisions  of  spinal  nerve.  15.  Conus  medullaris.  16,  16. 
Filum  terminales  internum.  17,  17.  Cauda  equina.  I-VIII.  Cervical  nerves.  I-XII.  Tho- 
racic nerves.    I-V.  Lumbar  nerves.    I-V.  Sacral  nerves. ; 

almost  to  a  point,  the  conus  medullaris;  but  a  very  small  process 
continues  in  the  f,lum  terminale  internum.  From  the  lumbar 
enlargement  rise  the  motor  fibers  of  the  nerves  contained  in  the 
lumbar  and  sacral  plexuses,  and  into  it  enter  the  sensory  fibers 
of  the  same  plexuses. 


THE    SPINAL    CORD. 


335 


Postero-lat.  sul 


Post,  median  sept. 
P.  I.  F.        I        Post,  intermediate  furrow 


Anterior  root  line 


Sixth  ventricle 


Gelatinous  substance 


Fig.  loi. — Sections  of  the  spinal  cord;  A.  The  cervical,  B.  The  thoracic,  C  The 
lumbar,  and  D.  The  sacral.     (Original.) 

A.  Section  of  cervical  cord.  A.  C.  Anterior  columna,  P.  C.  Posterior  columna,  C.  G.  Gray- 
commissure,  anterior  gray  and  posterior.  Com.  A.  White  anterior  commissure.  Fun.  Ant. 
Funiculus  anterior,  Fun  Lat.  Funiculus  lateralis.  Fun.  Post.  Funiculus  posterior.  G.  Fas- 
ciculus gracilis,  C.  Fasciculus  cuneatus.  B.  Section  of  thoracic  cord.  L.  C.  Lateral  columna. 
C.  Section  lumbar  cord.     D.  Section  of  lower  sacral  cord. 


THE    SPINAL    CORD,  337 

Sixth  Ventricle  (Fig.  loi,  B). — The  central  canal  of  the  spinal 
cord  {canalis  centralis  spinalis)  is  the  representative  of  the  ca\'ity 
of  the  neural  tube.  It  is  just  visible  to  the  naked  eye;  but  it 
extends  throughout  the  cord  and  expands  above  into  the  fourth 
ventricle.  In  the  filum  terminale  internum  it  is  also  dilated, 
forming  the  ventriculus  terminalis  (Krausei).  It  is  Hned  with 
columnar  ciliated  cells  wliich  stand  on  a  thick  lamina  of  substantia 
gelatinosa. 

Fissures  of  the  Spinal  Cord  (Fig.  loi). — The  spinal  cord 
is  incompletely  divided  into  symmetrical  lateral  halves  by  the 
anterior  and  the  posterior  median  fissure. 

The  anterior  median  fissure  {fissura  mediana  anterior)  is 
the  broader  and  shallower  of  the  two  (Fig.  loi).  It  extends  in 
length  from  the  inferior  end  of  the  ventral  surface  of  the  pons 
(foramen  caecum  of  Vicq  d'Azyr)  dov^ii  the  anterior  median  line 
of  the  medulla  and  cord.  As  to  depth,  it  equals  one-third  of  the 
cord's  axis.  Its  floor  is  formed  by  the  white  anterior  commissure. 
Both  layers  of  pia  mater  dip  do^\^l  into  it  and  inclose  the  anterior 
spinal  artery  and  its  branches.  The  anterior  median  fissure  is 
interrupted  at  the  junction  of  the  cord  and  medulla  by  the  decus- 
sation of  the  pyramids.  In  the  lumbar  enlargement  it  gradually 
disappears. 

The  posterior  median  fissure  [fissura  mediana  posterior) 
is  narrow  and  deep  (Fig.  loi).  It  extends,  longitudinally,  do^Mi 
the  posterior  median  hne  of  the  cord  from  the  middle  of  the 
posterior  surface  of  the  medulla.  It  divides  the  cord,  dorso- 
ventrally,  beyond  its  middle.  The  floor  of  the  fissure  is  formed 
by  the  posterior  commissure,  which,  with  the  gray  and  white 
anterior  commissures,  separates  the  posterior  from  the  anterior 
median  fissure.  The  posterior  median  fissure  is  not  an'  open 
fissure ;  it  is  occupied  by  a  lamina  of  connective  tissue,  the  posterior 
septum,  which  is  attached  to  the  deep  layer  of  the  pia  mater.  In 
the  posterior  septum  ramify  branches  of  the  two  posterior  spinal 
arteries  and  tributaries  of  the  external  spinal  veins. 

PosteriorLateral  Sulcus.  {S.  lateralis  posterior). — Each  lateral 
half  of  the  spinal  cord  is  partially  divided,  near  the  junction  of 
the  posterior  fourth  with  the  anterior  three-fourths  of  its  semi- 


338  THE    SPINAL    CORD. 

circumference,  by  the  posterior  lateral  sulcus  (Fig.  loi).  The 
sulcus  is  situated  opposite  the  posterior  columna  of  gray  matter, 
to  which  it  transmits  the  posterior  roots  of  the  spinal  nerves.  It 
is  continuous  above  with  the  posterior  lateral  sulcus  of  the  medulla. 
It  separates  the  posterior  surface  and  the  antero-lateral  surface 
from  each  other. 

Anterior  Root-line.  {S.  lateralis  anterior). — ^As  a  landmark, 
it  is  convenient  to  call  the  longitudinal  line  through  which  issue 
the  most  lateral  fibers  of  the  anterior  roots  of  the  spinal  nerves, 
the  anterior  root-line  of  the  spinal  cord  (Fig.  loi).  There  is  no 
groove  on  the  surface  of  the  cord  along  this  line  and  it  is  misleading 
to  call  it  a  sulcus,  as  has  been  the  custom.  It  is  situated  opposite 
the  anterior  columna  of  gray  matter  and  in  line  with  the  anterior- 
lateral  groove  of  the  medulla  oblongata.  Through  it  and  through 
the  surface,  just  medial  to  it,  emerge  the  anterior  roots  of  the 
spinal  nerves.  It  subdivides  the  antero-lateral  surface  into  ante- 
rior and  lateral  surfaces. 

The  posterior  intermediate  sulcus  (s.  intermedins  posterior) 
is  a  slight  longitudinal  groove  in  the  cord  which  subdivides  the 
upper  three-fourths  of  the  posterior  surface  into  postero-medial 
surface  and  postero-lateral  surface  (Fig.  loi).  From  it  a  con- 
nective tissue  septum  extends  into  the  cord  and  separates  the  fas- 
ciculus gracihs  and  fasciculus  cuneatus  from  each  other.  The 
posterior  intermediate  furrow  is  found  only  in  the  cervical  and 
in  the  upper  eight  thoracic  segments  of  the  cord. 

I.  GRAY  MATTER  OF  THE  CORD. 

The  spinal  cord  is  composed  of  (i)  gray  matter  (substantia 
grisea  spinahs),  in  the  central  part;  and  (2)  white  matter  (sub- 
stantia alba  spinalis)  in  the  peripheral  area.  It  is  like  the  medulla 
and  pons  in  having  the  white  matter  on  the  surface  (Fig.  loi). 

A  column  of  gray  matter  (Fig.  loi),  crescentic  in  section, 
extends  through  the  center  of  each  lateral  half  of  the  spinal  cord. 
The  crescent  is  convex  medially;  and  is  joined  to  its  fellow,  a 
little  in  front  of  the  middle,  by  a  vertical  transverse  lamina  of 
gray  matter,    called   the   gray   commissure    {commissura  grisea). 


GRAY  MATTER  OF  THE  CORD.  339 

It  is  joined  to  the  white  matter  of  the  opposite  side  by  the  white 
anterior  commissure.  The  points  of  the  crescent  are  directed 
forward  and  backward,  respectively,  and  form  the  anterior  and 
posterior  columnse.  A  lateral  projection  from  the  center  of  the 
crescent,  visible  only  in  the  thoracic  region,  is  called  the  lateral 
columna;  it  fuses  with  the  anterior  columna  in  the  cer\-ical  and 
and  lumbar  enlargements.  Together,  the  two  crescents  and  the 
gray  commissure  form  an  H-shaped  column  of  gray  matter.  The 
H-shaped  column  is  well  marked  in  the  cervical  and  thoracic 
regions;  but,  toward  the  lower  end  of  the  cord,  the  crescents  become 
short  and  thick,  and  the  gray  column  is  almost  cylindrical. 

The  H-shaped  column  is  composed  of  two  kinds  of  gray  sub- 
stance, viz.:  (i)  The  substantia  gelatinosa  (Rolandi),  which  forms 
(a)  a  cap  for  the  head  of  the  posterior  columna  and  (b)  an  en- 
velope for  the  central  canal,  or  ventricle,  of  the  cord.  (2)  The 
substantia  spongiosa.  The  latter  forms  all  the  H-shaped  column 
except  the  tips  of  the  posterior  columnas  and  the  thick  sheath  of 
the  central  canal.  Imbedded  in  the  neuroglia,  there  is  a  network 
of  medullated  nerve  fibers;,  and  these,  with  the  common  stains, 
give  rise  to  a  spongy  appearance  under  the  microscope. 

Gray  Crescent  (Fig.  loi). — ^It  is  made  up  of  (i)  the  anterior 
columna;  (2)  the  center,  which  is  joined  to  its  felloW'  of  the 
opposite  side  by  the  gray  commissure  and  which  forms  the  lateral 
projection,  called  the  lateral  columna;  and,  (3)  the  posterior 
columna.  The  lateral  border  of  the  crescent  is  not  everywhere 
clear  cut  and  definite,  especially  in  the  cervical  region,  but  is  inter- 
mingled for  a  short  distance  \^ith  the  white  matter,  forming  the 
formalio  reticularis.  The  formatio  reticularis  is  found  in  the 
cervical  region,  elsewhere  it  is  ver}-  feebly  developed. 

(i)  The  anterior  columna  (columna  anterior)  (Fig.  loi)  as 
seen  in  sections  is  short  and  thick  compared  with  the  posterior 
columna.  It  is  thickest  in  the  cersical  and  lumbar  enlargements, 
where  it  swells  out  sharply  toward  the  lateral  surface  of  the  cord; 
in  the  mid-thoracic  region  it  is  more  slender.  It  does  not  reach 
the  surface  of  the  cord  as  does  the  posterior  columna.  It  ends 
in  a  bulbous,  serrated  head,  which  points  toward  the  anterior 
root-line,  and  is  joined  to  the  center  of  the  crescent  by  the  cervix 


340  THE    SPINAL    CORD. 

or  base.  From  it  the  anterior  roots  of  the  spinal  nerves  rise;  and, 
together  with  the  anterior  root-fibers,  it  separates  from  each  other 
the  anterior  and  lateral  white  columns  of  the  cord. 

Cells  of  the  Anterior  Columna  (Figs.  102  and  103). — ^The  gray 
matter  of  the  spinal  cord  contains  multipolar  neurones  of  the 
Golgi  and  Deiters  types.  The  Golgi  cells  ramify  richly  in  the 
gray  matter  about  the  cell-bodies,  and,  both  their  axones  and 
dendrites  terminate  in  relation  with  other  neurones  in  the  adjacent 
gray  substance.  The  long  axones  of  the  Deiters  cells  either  enter 
into  the  anterior  roots  (radices  anterior),  and  the  neurones  are 
called  radicular  cells,  or  they  enter  into  a  longitudinal  tract  or 
strand  of  fibers,  and  the  neurones  are  named  strand-cells  (Cunning- 
ham). The  dendrites  of  the  Deiters  cells  arborize  in  both  the 
gray  and  white  substance.  The  cell-bodies  in  the  anterior  columna 
are  large  and  vesicular  in  character.  They  are  motor  or  efferent 
in  function,  and  their  axones  form,  in  great  part,  the  anterior  roots 
of  the  spinal  nerves.  Together  with  the  neurones  of  the  genetic 
nuclei  of  cerebral  nerves,  these  of  the  anterior  columna  constitute 
the  lower  segment  motor  neurones. 

Two  chief  columns  of  cell-bodies  are  located  in  the  anterior 
columna,  the  medial  column  and  the  lateral  column  (Figs. 
102  and  103).  The  former  is  continuous  throughout  the  cord  1 
with  the  exception  of  the  fifth  lumbar  and  the  first  sacral  segments 
(Bruce-Cunningham);  while  the  lateral  column  is  found  only 
in  the  cervical  and  lumbar  enlargements.  The  medial  column 
of  cells  shows  a  double  group  in  sections  of  the  lower  three  cer- 
vical, all  the  thoracic  and  the  first  lumbar  segments  of  the  cord. 
These  subgroups  are  called  the  ventro-medial  and  the  dorso- 
medial  cells.  Only  the  ventro-medial  group  is  present  above  the 
sixth  cervical  segment  and  below  the  first  lumbar  segment.  The 
dendrites  of  the  cell-bodies  in  the  medial  column  arborize  in  the 
gray  substance  of  the  same  columna,  in  the  adjacent  white  matter 
of  the  anterior  column  of  the  cord  and,  to  some  extent,  in  the 
opposite  anterior  columna,  having  passed  through  the  white  an- 
terior commissure;  the  axones  of  these  medial  cell-bodies  enter 
very  largely  into  the  anterior  roots  of  the  spinal  nerves  on  the 
same  side ;  but  a  certain  number  probably  run  through  the  white 


GRAY  MATTER  OF  THE  CORD. 


341 


Mid- cervical 
Fasciculus  gracilis 
Fasciculus  cuneatus 
Entry  zone 
Marginal  tract 


(Post.)  Cerebello 
spinal   fasciculus 


Antero-lat.  fascic 
ulus  proprius 

Medial  longitudinal  bundle 


Gelatinous  substance 


Dorso-lateral 
cells 


Ventro-lateral 
«     cells 


Ventro-medial  cells. 


Mid-thoracic 


Comma  tract 


Lateral  pyramidal 
£.,  tracti 

Rubro-spinal   tract 


Descending  ant. 

cerebello-spinal 

fasciculus 


Antero-lat.   fasciculus 
proprius 


Gelatinous  substance 


Nucleus  dorsalis 
(Clarki) 


Intermedio-lateral 
cells 


Dorso-medial  cells 


Anterior  pyramidal  tract 


Ventro-medial  cells 


Anterior  longitudinal  bundle 


Fig.  102. — Tracts  of  fibers  and  columns  of  cells,  in  the  cervical  and  thoracic  regions 
of^the  cord.     Diagrammatic.     (In  part  after  Bruce  and  Cunniugham.) 


GRAY   MATTER    OF    THE    CORD.  343 

anterior  commissure  into  the  anterior  nerve-roots  of  the  oppo- 
site side,  and  others  enter  into  the  fasciculi  proprii  of  the  cord. 
The  lateral  column  of  cells  in  the  anterior  columna  is  a  large 
one  (Figs.  102  and  103).  It  is  found  only  in  the  regions  which 
innervate  the  extremities,  that  is,  in  the  cervical  and  lumbar 
enlargements.  It  is  everywhere  divided  into  a  venlro-lateral  and  a 
dorso-lateral  cell-group,  and  in  most  of  the  segments  of  the  lumbar 
enlargement  there  are  two  other  cell-groups,  according  to  Alexander 
Bruce.  One  of  them  is  located  behind  the  dorso-lateral  cells 
and  is  called  the  post-dorso-lateral  group;  and  the  other,  which 
occupies  the  angle  between  the  ventro-lateral  and  the  dorso-lateral 
cells,  lying  medial  to  both,  is  called  the  central  group  (Cunning- 
ham). The  dendrites  of  the  cell-bodies  in  the  lateral  column 
arborize  and  end  both  in  the  gray  matter  of  the  anterior  columna 
and  in  the  white  matter  adjacent  to  its  lateral  surface;  the  axones 
proceed  largely  into  the  anterior  roots  of  the  spinal  nerves  but  partly 
into  the  longitudinal  white  columns  of  the  cord.  Probably  the 
medial  column  innervates  the  trunk  muscles;  the  lateral  column, 
the  muscles  of  the  extremities.  Cortical  Connection. — ^These 
cell-columns  are  brought  into  relation  with  the  anterior  (direct) 
pyramidal  fibers  and  the  lateral  (crossed)  pyramidal  fibers  by 
means  of  intermediate  neurones.  In  this  manner  motor  and 
inhibitory  impulses  descend  to  them  from  the  cerebral  cortex, 
coming  from  the  opposite  hemisphere,  chiefly,  but  also  from  the 
same  side.  They  also  are  in  relation  with  the  end-tufts  of  posterior 
root-fibers  and  \\dth  axones  whose  cell-bodies  are  located  in  the 
center  and  posterior  columna  of  the  gray  crescent.  The  latter 
neurones  form  contact  relations  mth  fibers  of  the  posterior  roots 
of  the  spinal  nerves  on  both  sides.  Thus  both  by  immediate 
contact  between  anterior  and  posterior  root-neurones  and  by  the 
intervention  of  an  intrinsic  spinal  neurone  the  simple  reflex  mechan- 
ism of  the  spinal  cord  is  formed.  It  has  been  the  beHef  that  the 
end-tufts  of  the  fibers  in  the  anterior  and  lateral  pyramidal  tracts 
are  in  direct  contact  with  the  dendrites  or  cell-bodies  of  the  neu- 
rones in  the  anterior  columna;  but  the  investigations  of  Schiifer, 
ColHer  and  others,  indicate  that  this  connection  between  the 
neurones  of  the  anterior  columna  and  the  lateral  pyramidal  fibers. 


344  THE    SPINAL    CORD. 

at  least,  is  established  by  intervening  neurones  whose  cell-bodies 
are  located  near  the  base  of  the  posterior  columna  in  the  region 
of  the  nucleus  dorsalis  (Clark's  column).  The  evidence  of  such 
termination  of  the  anterior  pyramidal  tract  is  not   conclusive. 

Lesions. — ^Paralysis  due  to  lesions  of  the  anterior  columna 
and  of  the  genetic  nuclei  of  cerebral  nerves  is  often  called  lower 
segment  paralysis.  The  cells  in  the  anterior  columna  are  the  seat 
of  hemorrhagic  inflammation  and  rapidly  degenerate  in  acute 
anterior  poliomyelitis.  In  progressive  muscular  atrophy  and 
in  amyotrophic  lateral  sclerosis  they  degenerate  slowly.  As  a 
result  of  the  first,  sudden  flaccid  paralysis  occurs.  The  muscles 
waste  away  in  the  second  and  third  because  the  nerves  controlling 
the  muscles  and  their  blood  supply  are  gradually  destroyed.  In 
the  last,  the  muscles  are  also  spastic,  because  the  involvement 
of  the  pyramidal  tracts  cuts  off  cerebral  inhibition. 

(2)  Center  of  Crescent  and  Columna  Lateralis  (Fig.  loi). — 
In  the  center  of  the  crescent  there  are  many  small,  closely  packed 
cell-bodies,  which  are  probably  sympathetic  in  function.  This  part 
of  the  crescent  appears  to  contain  the  automatic  spinal  centers, 
such  as,  the  cilio-spinal,  cardiac-accelerator,  vaso-motor,  secre- 
tory, trophic,  inhibito-secretory,  viscero-motor,  viscero-inhibitory, 
etc.  That  the  cell-bodies  in  the  center  of  the  crescent  are  of 
sympathetic  junction  is  suggested  by  two  facts ;  -first,  the  cell-bodies 
are  small,  which  indicates  that  the  axones  run  but  a  short  dis- 
tance from  the  neurone  center,  as  is  the  case  with  spinal  sympa- 
thetic neurones;  and,  second,  the  distribution  of  these  central 
neurones  is  limited  to  those  regions  of  the  spinal  cord  whence 
the  efferent  sympathetic  fibers  rise. 

The  intermedio -lateral  column  of  cell-bodies  (Fig.  102,  B)  is 
the  only  one  found  in  the  center  of  the  crescent.  In  the  thoracic 
segments  of  the  cord,  where  the  lateral  columna  is  visible,  this 
column  is  contained  in  the  lateral  columna  and  in  the  white  matter 
immediately  adjacent  to  it;  so  far  as  it  is  found  in  the  cervical 
and  lumbar  enlargements  it  is  situated  in  the  base  of  the  anterior 
columna  near  its  lateral  surface.  The  intermedio-lateral  column 
is  found  in  the  last  cervical,  all  the  thoracic  and  the  first  and  second 
lumbar  segments,  in  a  nearly  continuous  column;  it  is  also  found 


GRAY  MATTER  OF  THE  CORD. 


345 


Third  lumbar  segment 


Posterior  column 
Entrj'  zone 
Marginal  tract 
(Lissaueri) 


Spino-thala- 
mic  tract 


Triangular  tract 
(Helwigi) 

Medial  longitudinal  bundle 


Oval  tract  (Flechsigi) 

Gelatinous  substance- 


Cells  of  post, 
columna 


Central  cells 


Ventro-lateral  cells 
Ventro-medial  cells 


Third  sacral  segment 


Septomarginal  tract 
Postero-lateral    descending    tr 
Cornu-commissural  tr 
Lateral  pyramidal  tr 


Bandalette  of  hoche 

Gelatinous  substance 


Antero-lat.  fas- 
ciculus proprius 

Descending  ant. 

cerebello-spinal  tract 


Dorso  -  latera 
cells 


Anterior  pyramidal  tract 


Central  cells 


Ventrol  lateral  cells 
Anterior  longitudinal  bundle 


Fig.   103. — Tracts  of  fibers  and  columns  of  cells  in  the  lumbar  and  sacral  regions 
of  the  cord.     Diagrammatic.  (In  part  after  Bruce  and  Cimuingham.) 


GRAY  MATTER  OF  THE  CORD.  347 

in  the  third  and  fourth  sacral  segments  of  the  cord  and  in  the 
first  three  cervical  (Cunningham).  The  first  region  (from  last 
cervical  to  second  lumbar  segment)  corresponds  in  position  and 
extent  to  the  origins  of  the  white  rami  communicantes ;  the  second 
region  is  at  the  level  of  origin  of  the  pelvic  splanchnics;  and  the 
cell-groups  representing  this  column  in  the  upper  cervical  seg- 
ments probably  contribute  sympathetic  fibers  to  the  accessory 
and  phrenic  nerves. 

The  cells  of  the  intermedio-lateral  column  are  largely  of  the 
radicular  variety,  their  slender  axones  enter  into  the  anterior 
roots  of  the  spinal  nerves.  Whether  any  belong  to  the  strand- 
variety  is  not  known.  They  are  in  contact  relation  with  posterior 
root-fibers  and  are  also  connected  with  the  posterior  roots  by 
intervening  neurones.  Their  cerebral  connection  has  not  been 
traced. 

(3)  The  posterior  columna  {columna  posterior)  except  in  the 
lower  cord,  is  slender  (Fig.  loi).  It  is  longer  than  the  anterior 
columna  and  reaches  the  surface  in  the  posterior  lateral  sulcus, 
where  it  receives  the  posterior  roots  of  the  spinal  nerves.  The 
posterior  columna  presents  a  slight  enlargement  near  its  extrem- 
ity, called  the  caput  columnce,  which  tapers  off  to  the  apex 
columncB.  The  head  is  joined  to  the  base  by  a  constricted  part, 
the  cervix.  The  head  of  the  posterior  columna  is  capped  by  a 
V-shaped  mass  of  substantia  gelatinosa.  Spongy  substance  makes 
up  the  remainder  of  it.  The  posterior  columna  separates  the 
posterior  from  the  lateral  column  of  the  cord  (Figs.  102  and  103). 

The  cells  0}  the  posterior  columna  are  numerous.  In  the  head 
of  the  posterior  columna  they  have  smaller  bodies  than  the  cells 
of  the  columna  anterior.  They  are  less  definitely  grouped  and 
are  fusiform  in  shape  throughout  the  caput  columnce;  but  in  the 
base  of  the  horn,  near  its  medial  surface,  they  have  large  vesicular 
bodies  and  form  one  of  the  most  definite  cell-columns  in  the 
spinal  cord.  The  posterior  columna  neurones  are  aft'erent  or 
sensory  in  function. 

The  neurones  of  the  head  of  the  posterior  columna  (Figs.  102 
and  103)  belong  largely  to  the  type  of  Golgi,  as  the  processes  of 
the  greater  number  of  them  neither  enter  into  the  anterior  roots 


348  THE    SPINAL    CORD. 

of  the  spinal  nerves,  nor  help  to  form  the  longitudinal  fiber-tracts 
of  the  cord.  Their  axones  arborize  and  end  in  the  gray  substance 
of  both  crescents.  Those  axones  of  the  Golgi  cells  which  cross 
over  through  the  posterior  commissure  to  the  opposite  crescent 
help  to  constitute  the  "immediate  decussation"  of  the  pain  and 
temperature  path.  There  are  also  Deiters  cells  in  the  head  of  the 
posterior  columna;  their  axones  enter  into  the  posterior  fasciculus 
proprius  of  the  cord,  hence  they  belong  to  the  strand-variety. 
They  appear  to  form  the  ventral  field  of  the  posterior  column 
(Hoche)  called  the  cornu-commissural  tract,  and  at  least  a  part 
of  the  comma,  oval  and  septo-marginal  tract.  The  neurones 
in  the  caput  of  the  posterior  columna  receive  posterior  root-fibers 
which  carry  excito-reflex  impulses  and  impulses  of  the  tactile, 
pain  and  temperature  senses.  The  former  are  transmitted  for- 
ward largely  in  the  same  crescent  to  the  center  and  anterior  columna ; 
the  latter,  to  a  considerable  extent,  are  carried  through  the  pos- 
terior commissure  to  the  anterior  columna  of  the  opposite  cres- 
cent. 

Nucleus  Dorsalis  (Stillingi  and  Clarki). — ^This  column,  which 
was  discovered  by  Stilling,  is  composed  of  cell-bodies  measuring 
from  40//  to  9o«  in  diameter  (Figs.  102  and  104).  It  forms  a 
most  striking  feature  of  the  gray  crescent  throughout  the  thoracic 
region.  It  is  situated  near  the  media!  surface  of  the  base  of  the 
posterior  columna,  bounded  laterally  by  a  curved  strand  of  pos- 
terior root-fibers ;  and  forms  a  continuous  column  from  the  seventh 
cervical  segment  to  the  second  lumbar  segment.  The  column 
is  largest  in  the  lower  two  thoracic  segments,  where  it  bulges  out 
the  medial  surface  of  the  posterior  columna.  It  is  represented 
by  separated  groups  of  cell-bodies  in  the  third  and  fourth  sacral 
and  first  three  or  four  cervical  segments  of  the  cord  and  in  the 
accessory  nucleus  of  the  cuneate  column  in  the  medulla  oblongata. 
The  limitation  of  the  dorsal  nucleus,  as  an  unbroken  column, 
to  the  region  of  the  white  rami  communicantes  has  suggested  its 
connection  with  the  sympathetic  system ;  and  it  is  the  terminal  nu- 
cleus of  afferent  sympathetic  fibers,  but  it  gives  rise  to  no  efferent  fibers 
of  that  system.  All  the  axones  of  the  dorsal  nucleus  appear  to 
run  toward  the  lateral  surface  of  the  cord  and  enter  into  the  cere- 


GRAY  MATTER  OF  THE  CORD. 


349 


bello-spinal  tract  of  the  same  side.  The  several  dendrites  of  each 
neurone  ramify  richly  in  the  vicinity  of  the  cell-body.  Together 
with  the  cell-bodies,  the  dendrites  are  in  contact  relation  with 
fibers  of  the  posterior  roots  of  the  spinal  nerves.  The  nucleus 
dorsalis  probably  has  to  do  with  muscular  tonicity  and  equilibrium, 
chiefly.  It  is  supposed  to  receive  afferent  sympathetic  impulses 
from  the  internal  organs. 

Concerning  the  relation  of  the  gray  crescent  to  the  spinal  nerves 
(Fig.  104),  it  may  be  remarked,  here,  that  in  the  anterior  columna 


Posterior  root 


Posterior  median  fissure 

Fibers  to  medulla 


Fibers  to  mar- 
ginal tract 


Anterior  root  Anterior  median  fissure 

Fig.   104. — The  roots  of  the  spinal  nerves.     Diagrammatic.     (Original.) 

Anterior  root  rises  from  medial,  lateral  and  intermedio-lateral  cells  of  same  crescent  and 
from  medial  cells  of  opposite  crescent:  it  is  also  connected  with  the  opposite  side  by  certain 
dendrites. 

Posterior  root  terminates  in  gelatinous  substance,  in  the  center  and  base  of  the  posterior 
columna,  in  the  intermedio-lateral  column,  and  in  the  anterior  columna  of  the  same  crescent ; 
in  the  anterior  and  posterior  columna  of  the  opposite  side  ( ?) ;  and  in  the  nucleus  funiculi  gra- 
cilis or  nucleus  funiculi  cuneati  of  the  medulla  oblongata. 


and  center  of  the  crescent  are  located  the  genetic  nuclei  of  the 
motor  or  efferent  fibers  (anterior  roots)  of  the  spinal  nerves; 
and  that  the  terminal  nuclei  of  the  sensory  fibers  (posterior  roots) 
of  the  spinal  nerves  are  located  chiefly  in  the  posterior  columna, 
but  also  in  the  center  and  anterior  columna  of  the  crescent  in  the 
cord,  and  in  the  nucleus  funiculi  gracilis  and  nucleus  funiculi 
cuneati  in  the  medulla  oblongata. 


35©  THE    SPINAL    CORD. 

The  gray  commissure  of  the  spinal  cord  (the  gray  anterior, 
and  the  posterior  commissure)  is  the  vertical,  transverse  sheet  of 
gray  substance  connecting  the  two  crescents  together  (Fig.  loi). 
This  commissure  (commissura  grisea)  completes  the  gray  matter 
of  the  cord.  It  unites  the  gray  crescents  together  a  little  in  front 
of  their  center,  except  in  the  lumbar  region  where  it  joins  their 
centers.  It  forms  the  floor  of  the  posterior  median  fissure;  and, 
in  front,  is  in  relation  with  the  white  anterior  commissure.  It 
is  pierced  longitudinally  by  the  central  canal  of  the  spinal  cord, 
which  is  surrounded  by  a  thick  envelope  of  substantia  gelatinosa. 
This  canal,  the  sixth  ventricle,  divides  the  commissure  into  two 
parts.  That  part  of  the  commissure  in  front  of  the  canal  is  the 
gray  anterior  commissure  (commissura  anterior  grisea)  and  that 
behind  it  is  ^  the  posterior  commissure  {commissura  posterior,  Fig. 
loi).  The  gray  commissure,  comprising  both  these  divisions, 
is  composed  of  spongy  and  gelatinous  substance  in  which  there 
are  imbedded  the  bodies  of  many  nerve  cells  and  a  large  number 
of  medullated  fibers.  The  medullated  fibers  are  derived  from 
the  posterior  roots  of  the  spinal  nerves,  and  from  intrinsic  neu- 
rones of  the  cord,  whose  centers  are  situated  chiefly  in  the  commis- 
sure and  in  the  posterior  columna.  The  posterior  commissure 
is  said  to  contain  a  long  sensory  tract,  between  the  ventricle  and 
dorsal  surface  (Ciaglinski).  This  long  sensory  tract  is  found  in 
the  thoracic  portion  of  the  cord  and  the  discoverer  believes  it  to 
be  made  up  of  ascending  root-fibers  which  conduct  pain  and 
temperature  impulses.  It  is  in  need  of  further  investigation 
(Barker). 

Lesions  of  the  gray  substance,  as  in  syringomyelia,  completely 
abolish  the  pain  and  temperature  senses  at  the  level  of  the  lesion, 
while  the  muscular  and  tactile  senses  are  preserved.  The  dis- 
sociation of  sensations  is  most  complete  and  bilateral  when  the 
lesion  destroys  the  posterior  commissure;  if  the  lesion  be  limited 
to  one  crescent,  the  pain  and  temperature  senses  are  affected  on 
the  side  opposite  to  the  lesion.  These  facts  show  that  the  pain 
and  temperature  paths  to  the  cerebral  cortex  run  through  the  gray 
substance  of  the  cord  and  that  they  decussate  through  it  imme- 
diately upon  entering  the  cord.     It  also  shows  that  muscular  and 


WHITE    MATTER    OF    THE    CORD.  35 1 

tactile  impressions  may  reach  the  cerebrum  without  passing  through 
the  gray  substance  in  the  spinal  cord;  but  it  docs  not  exclude  the 
possibility  of  a  part  of  the  impulses  of  the  muscular  and  tactile 
senses  being  transferred  from  a  lower  to  a  higher  neurone  in  the 
spinal  gray  substance. 

2.     WHITE  MATTER  OF  THE  CORD. 

The  white  matter  (Fig.  loi)  of  the  spinal  cord  (substantia  alba 
spinalis)  is  disposed  in  its  peripheral  area  and  in  the  white  ante- 
rior commissure.  It  is  composed  of  medullated  nerve  fibers 
(axones  and  collaterals)  imbedded  in  a  small  amount  of  neuroglia, 
and  supported  by  a  connective  tissue  network  derived  from  the 
pia  mater.  Like  the  gray  matter,  it  is  richly  supplied  with  blood- 
vessels. The  fibers  of  the  spinal  cord  run  transversely,  dorso- 
ventrally  and  longitudinally. 

The  transverse  fibers,  which  are  usually  somewhat  oblique 
in  direction,  comprise  (i)  those  running  from  the  longitudinal 
tracts  into  the  gray  matter  or  out  of  the  gray  matter  into  such 
tracts;  (2)  the  axones  of  intrinsic  neurones  which  connect  the  two 
crescents  at  nearly  the  same  level;  and  (3)  posterior  root-fibers 
running  through  the  posterior  commissure  to  the  opposite  crescent. 

The  white  anterior  commissure  of  the  spinal  cord  {commissura 
anterior  alba)  is  the  only  definite  lamina  of  transverse  fibers  in 
the  cord  (Fig.  loi).  It  connects  the  anterior  and  lateral  white 
columns  of  the  cord  with  the  opposite  gray  crescent  and  the  two 
crescents  with  each  other.  It  is  located  in  front  of  the  gray  an- 
terior commissure,  forming  the  floor  of  the  anterior  median  fissure. 
It  is  composed  of  medullated  fibers  belonging  to  (a)  the  anterior 
pyramidal  tract,  (b)  the  anterior  fasciculus  proprius,  (c)  the  as- 
cending anterior  cerebello-spinal  and  spino-thalamic  tracts;  (d)  it 
comprises  the  crossed  fibers  to  the  anterior  roots  of  the  spinal 
nerves,  and  (e)  the  decussating  dendrites  between  the  anterior 
columnas. 

The  dorso-ventral  fibers  of  the  spinal  cord  (Fig.  104)  are 
(a)  those  of  the  anterior  roots  of  the  spinal  nerves,  in  their  course 
from  the  gray  matter  to  the  surface  of  the  cord;  (b)  those  of  the 


352  THE    SPINAL    CORD. 

posterior  roots,  running  from  the  posterior-lateral  sulcus  to  their 
destination  in  the  gray  matter,  and  (c)  axones  of  intrinsic  neu- 
rones connecting  posterior  with  anterior  parts  of  the  crescent. 

The  longitudinal  fibers  comprise  most  of  the  white  matter 
in  the  cord,  forming  the  funiculus  anterior,  funiculus  lateralis 
and  funiculus  posterior  (Fig.  loi).  These  three  great  columns 
occupy  the  anterior,  lateral  and  posterior  areas  of  the  cord.  They 
are  disposed  around  the  gray  crescent  in  bundles  or  tracts.  The 
tracts  which  make  up  the  funiculi  are  not  visible  to  the  naked 
eye,  nor  under  the  microscope  in  a  healthy  adult  cord;  they  have 
been  located  by  embryological,  experimental  and  pathological 
investigations.  The  longitudinal  fibers  rise  in  the  brain,  in  the 
spinal  cord  and  in  the  spinal  ganglia ;  some  run  upward  and  others 
downward,  constituting  the  tracts  of  the  cord.  Thus  the  tracts 
are  characterized  as  ascending,  descending  and  mixed  tracts. 

Ascending  Tracts:  (i)  Ascending  anterior  cerebello-spinal 
and  spino-thalamic  tract.  (2)  Cerebello-spinal  tract  (direct  cere- 
bellar) with  the  spino-vestibular  tract.  (3)  Marginal  tract  (of 
Lissauer).  (4)  Fasciculus  cuneatus.  (5)  Fasciculus  gracilis.  (6) 
Ciaglinski's  long  sensory  tract,  in  the  posterior  commissure. 
'Descending  Tracts:  (i)  Anterior  (direct)  pyramidal  tract, 
including  the  anterior  longitudinal  bundle.  (2)  Lateral  (crossed) 
pyramidal  tract.  (3)  Descending  anterior  cerebello-spinal  tract, 
including  Helwig's  tract.  (4)  Rubro-spinal  tract  (Pawlow).  (5) 
Descending  postero-medial  tract,  called  at  different  levels  the 
comma,  oval,  and  septo-marginal  tract.  (6)  Descending  postero- 
lateral tract. 

Mixed,  Ascending  and  Descending  Tracts:  (i)  The  ante- 
rior fasciculus  proprius,  includiug  the  medial  longitudinal  bundle. 
(2)  Lateral  fasciculus  proprius.  (3)  The  posterior  fasciculus 
proprius,  composed  of  the  comu- commissural  tract,  the  septal 
bandalette  of  Hoche,  and  possibly  a  part  of  the  comma,  oval, 
septo-marginal  and  the  descending  postero-lateral  tract  (Cun- 
ningham). 

The  methods  of  locating  tracts  of  fibers  may  be  summarized 
briefly,  as  follows: 

The  embryological  method  was  first  employed  successfully 


TRACTS    OF    THE    SPINAL    CORD.  353 

by  Flechsig.  He  found  that  nerve  fibers  when  first  laid  down  are 
naked  axones  without  any  insulating  white  substance  of  Schwann 
ensheathing  them.  That  tlic  medullary  sheaths  arc  developed 
at  different  times  and  that  the  medullation  is  nearly  coincident 
with  the  beginning  of  function.  Thus  the  fibers  of  motor  and 
sensory  nerves  are  f^rst  to  become  medullated,  since  life  cannot  be 
sustained  without  the  automatic  mechanism.  Second,  the  fascic- 
uli proprii  of  the  cord  are  medullated  and,  ihird,  the  cerebellar 
tracts.  At  this  stage  the  simple  automatic  and  coordinating  mech- 
anisms are  complete.  Fourth,  the  voluntary  motor  mechanism 
is  estabhshed  by  the  medullation  of  the  tracts  connecting  the 
lower  neurones  vdth  the  cerebral  cortex,  the  fibers  of  the  pyram- 
idal tracts  being  the  last  to  receive  their  medullar}^  sheaths. 
This  last  occurs  just  before  birth.  Fibers  of  the  cerebrum  con- 
cerned with  the  higher  psychic  functions  of  the  brain  become  med- 
ullated gradually,  year  after  year,  keeping  pace  with  the  mental 
development;  and  the  process  of  medullation  there  is  not  com- 
pleted until  late  in  life  (Kaes). 

The  pathological  and  experimental  methods  depend  upon 
the  fact  that  a  nerve  fiber  when  severed  from  the  cell-body  under- 
goes degeneration  in  accordance  with  the  law  of  Waller.  If  the 
severed  fiber  be  above  the  cell-body,  the  degeneration  occurs 
above  the  lesion  and  is  called  ascending  degeneration;  but,  if 
the  degeneration  extends  from  the  lesion  down  the  nerve  fiber, 
the  cell-body  being  above,  then  the  condition  is  called  descending 
degeneration,  though  all  parts  of  the  severed  fibers  really 
degenerate  simultaneously.  Thus  by  studying  the  paths  of  de- 
generation, above  and  below  a  destructive  lesion  in  the  human 
cerebro-spinal  axis,  the  various  tracts  of  fibers  have  been  discov- 
ered and  many  of  them  charted  and  traced  from  origin  to  termin- 
ation. These  investigations  have  been  greatly  aided  by  the 
study  of  degenerations  in  the  brain  and  cord  of  lower  animals. 
These  degenerations  are  the  results  of  definite  experimental  lesions, 
as  cutting  of  certain  posterior  nerv'e  roots,  partial  section,  hemi- 
section  or  complete  section  of  the  spinal  cord,  etc.  The  patho- 
logical and  experimental  methods  are  commonly  called  the  physio- 
logical method. 
23 


354  THE    SPINAL    CORD. 

TRACTS  OF  THE  SPINAL  CORD. 

The  antero-lateral  fasciculus  proprius  {fasciculus  antero- 
lateralis  proprius)  occupies  the  deep  part  of  the  anterior  and  lateral 
columns  (Figs.  102  and  103).  It  embraces  the  anterior  columna 
of  gray  matter  and  covers  the  outer  surface  of  the  center  of  the 
crescent  and  the  base  of  the  posterior  columna.  By  the  most 
lateral  anterior  root-fibers  it  is  subdivided  into  anterior  and  lateral 
fasciculi.  It  approaches,  but  does  not  quite  reach,  the  surface 
of  the  cord.  Notice  that  it  is  separated  from  the  anterior  median- 
fissure  by  the  anterior  pyramidal  tract,  and  that  the  anterior  cere- 
bello-spinal  and  spino-thalamic  tracts  run  between  it  and  the 
surface  of  the  cord.  Behind,  it  is  in  relation  with  the  lateral  pyram- 
idal tract.  The  antero-lateral  fasciculus  proprius  is  composed 
of  ascending  and  descending  fibers  which  are  the  T-branches 
of  axones  from  the  gray  crescent.  It  is  largely  a  short  fiber  tract, 
associative  and  commissural  in  function.  That  part  situated  in 
the  anterior  column,  the  anterior  fasciculus  proprius,  is  largely 
commissural,  between  the  anterior  columnse;  while  the  lateral 
fasciculus  proprius  is  chiefly  associative,  and  connects  different 
segments  of  the  cord  on  the  same  side.  The  antero-lateral  fas- 
ciculus proprius  is  continued  in  the  substantia  reticularis  of  the 
medulla,  and  the  reticular  formation  of  pons  and  mid-brain, 
constituting  a  short  fiber  tract  which  extends  from  the  lower  part 
of  the  cord  to  the  basal  gangha  of  the  cerebrum.  In  the  anterior 
fasciculus  proprius  there  is  a  strand  of  long  fibers  called  the  me- 
dial longitudinal  bundle  {fasciculus  longitudinalis  medialis). 

The  medial  {posterior)  longitudinal  bundle  is  composed  of  an 
ascending  and  a  descending  strand  of  fibers  (Figs.  102  and  103). 
The  ascending  strand  rises  from  the  anterior  columna  in  each 
segment  of  the  spinal  cord  and  runs  upward  to  the  motor  nuclei 
of  cerebral  nerves  and  terminates  in  them.  Perhaps  a  few  fibers 
reach  the  thalamus.  It  ascends  just  ventro-medial  to  the  anterior 
columna  in  the  cord;  in  the  medulla,  it  runs  between  the  head 
of  the  anterior  columna  and  the  pyramidal  decussation,  then  just 
lateral  to  the  fillet  decussation,  after  which,  it  takes  its  dorso-medial 
position  along  the  raphe.     Its  function  is  reflex.     The  descending 


TRACTS    OF    THE    SPINAL    CORD.  355 

strand  is  the  medial  ponlo-spinal  tract  (Collieri).  It  rises  from 
all  the  nuclei  of  the  reticular  formation  but  chiefly  from  the  nu- 
clei centrales  and  the  nucleus  laterahs  medius  in  the  pons.  Form- 
ing a  part  of  the  medial  longitudinal  bundle  of  the  same  side, 
its  fibers  end  in  the  center  of  the  crescent  as  it  descends  the  cord. 
Witliin  the  lateral  fasciculus  proprius,  descends  the  lateral  ponlo- 
spinal  tract  (Collieri).  This  tract  has  the  same  origin  and  termina- 
tion as  the  medial  ponto-spinal  tract  except  that  it  decussates.  It 
crosses  near  its  origin  right  through  the  medial  longitudinal  bundles. 
Both  ponto-spinal  tracts  extend  to  the  lower  part  of  the  cord. 

The  anterior  pyramidal  tract  {fasciculus  cerebro-spinalis 
anterior),  occupies  a  thin  area  next  the  anterior  median  fissure 
(Figs.  102  and  103).  It  is  the  direct  continuation  of  about  10  per 
cent,  of  the  pyramidal  tract  in  the  medulla.  Its  fibers  are  axones 
of  cortical  cells  whose  bodies  are  situated  in  the  anterior  central 
g}'rus  of  the  cerebrum.  As  the  tract  descends  in  the  cord,  the 
fibers  decussate  through  the  white  anterior  commissure,  and  ter- 
minate in  relation  with  the  cells  of  the  opposite  gray  crescent,  prob- 
ably, in  the  posterior  columna.  It  reaches  to  the  fifth  sacral 
segment  (Colher).  Imbedded  in  the  anterior  pyramidal  tract 
is  a  small  strand  first  described  by  Held,  the  anterior  longitudinal 
bundle. 

Anterior  Longitudinal  Bundle  (Figs.  102  and  103). — Held  called 
it  the  fasciculus  longitudinalis  ventralis.  It  occupies  a  very  nar- 
row strip  in  the  anterior  column  just  beside  the  entrance  of  the 
anterior  median  fissure.  The  anterior  longitudinal  bundle  has 
already  been  traced  from  its  origin  in  the  superior  quadrigeminal 
colHculus,  through  the  dorsal  tegmented  decussation  (Meynerti) 
to  a  position  in  the  mid-brain  ventro-lateral  from  the  medial 
longitudinal  bundle.  It  descends  in  that  relative  position  through 
the  pons  and  half  the  medulla;  near  the  pyramidal  decussation 
the  anterior  and  medial  longitudinal  bundles  are  brought  together 
and  he  between  that  decussation  and  the  isolated  head  of  the  an- 
terior columna;  they  diverge  upon  entering  the  cord  and  remain 
separate  to  the  end.  The  anterior  longitudinal  bundle  ends  in 
both  anterior  columnae  (Colher).  It  forms  the  middle  link  in 
the  ocular  and  pupillary  reflex  arcs. 


356  THE    SPINAL    CORD. 

The  descending  anterior  cerebello-spinal  tract  (fasciculus 
descendens  cerebello-spinalis  anterior — ^Marchi's,  Tschermak's  and 
Loewenthal's  column)  together  with  the  ascending  anterior  cere- 
bello-spinal tract,  occupies  a  thin  peripheral  area,  broadest  poste- 
riorly, which  extends  from  the  anterior  pyramidal  tract  outward 
and  backward,  over  the  antero-lateral  fasciculus  proprius,  to  the 
middle  of  the  lateral -surf ace  of  the  cord  (Figs.  102  and  103).  Its 
posterior  border  is  in  relation  with  the  (posterior)  cerebello-spinal 
tract  and  the  lateral  pyramidal  tract.  The  fibers  of  the  two  an- 
terior cerebello-spinal  tracts  are  mingled  together;  but  the  de- 
scending fibers  are  found,  chiefly,  in  the  anterior  and  postero- 
medial part  of  the  common  area  and  the  ascending  in  the  postero- 
lateral part.  The  tract  is  almost  completely  relayed  in  the  me- 
dulla. The  descending  fibers,  in  the  first  stage,  are  axones  from 
the  cortical  cells  of  Purkinje  in  the  cerebellum  and  from  the  nucleus 
fastigii  and  perhaps  the  other  cerebellar  ganglia.  They  descend 
to  the  nucleus  of  Deiters  through  the  brachium  pontis  cerebelli. 
There  the  greater  number  end  and  new  fibers  rise  which  continue 
the  tract  down  the  cord.  In  all  probability  the  cerebello-olivary 
fibers  in  the  restiform  body,  and  the  olivo-spinal  fibers,  forming 
the  tract  of  Helwig  in  the  cord,  should  be  included  in  the  descend- 
ing cerebellar  tract'.  It  terminates  in  the  gray  substance  of  the 
spinal  cord  and  directly  or  by  the  intervention  of  intrinsic  spinal 
neurones  is  connected  with  the  motor  cells  of  the  anterior  col- 
umna.  The  descending  cerebello-spinal  tract  forms  one  segment 
of  an  indirect  motor  path;  and,  together  with  the  intrinsic  and 
anterior  columna  neurones,  it  forms  the  efferent  limb  of  a  reflex 
arc  of  muscular  tonicity,  coordination  and  equilibrium.  Scattered 
among  the  vestibolu-spinal  fibers  in  the  posterior  part  of  the 
anterior  descending  cerebello-spinal  tract  are  descending  fibers 
from  the  thalamus  and  quadrigeminal  colliculi  which  end  in  the 
gray  crescent. 

Ascending  Anterior  Cerebello-spinal  and  Spino-thalamic 
Tract.  {Fasciculus ascendens  cerehello- spinalis  anterior,  Gowersi). — 
These  form  a  single  tract  in  the  cord  which  is  found  chiefly  in  the 
postero-lateral  part  of  the  area  common  to  it  and  the  descending 
anterior  cerebello-spinal  tract  (Figs.  102  and  103).     It  is  composed 


TRACTS  OF  THE  SPINAL  CORD.  357 

of  axonic  processes  of  cells  whose  bodies  are  situated  in  the  center 
of  the  crescent  and  base  of  the  anterior  columna,  chiefly  on  the 
opposite  side  of  the  cord  (v.  Lenhossek).  Most  of  the  fibers  of 
the  ascending  anterior  cerebello-spinal  and  spino-thalamic  tract 
cross  near  their  origin  through  the  white  anterior  commissure  of 
the  cord.  In  the  medulla,  the  tract  ascends  through  the  dorsal 
part  of  the  lateral  area,  sending  collaterals  to  the  inferior  lateral 
nucleus;  it  then  continues,  through  the  formatio  reticularis  of  the 
pons,  to  a  point  near  the  inferior  quadrigeminal  colliculus,  where 
the  cerebellar  part  is  bent  backward  under  the  brachium  conjunc- 
tivum,  and  enters  the  vermis  cerebelli  superior  through  the  superior 
medullary  velum  (Hoche).  The  spino-thalamic  portion  con- 
tinues to  the  thalamus,  sending  some  fibers  to  the  quadrigeminal 
colHculi  (Mott)  and  others  to  the  substantia  nigra  and  lentiform 
nucleus  (Rossolimo).  The  anterior  ascending  cerebello-spinal 
and  spino-thalamic  tract  carries  tactile,  pain,  and  temperature 
impulses.  The  triangular  tract  of  Helwig  (fasciculus  olivaris) 
is  found  on  the  surface  near  the  middle  of  the  area  common  to  the 
anterior  cerebello-spinal  tracts  (Figs.  102  and  103).  It  descends 
just  lateral  to  the  anterior  nerve  roots  and  may  be  traced  to  the 
lumbar  region,  where  its  longest  fibers  end.  It  probably  rises 
in  the  oUve  of  the  medulla  oblongata  and  is  efferent  in  conduction. 
The  (posterior)  cerebello-spinal  tract  {direct  cerebellar) 
{fasciculus  cerebello-spinalis  [posterior^)  runs  posterior  to  the 
other  cerebello-spinal  tracts  (Fig.  102).  It  is  superficially  located, 
and  in  section  extends  from  the  middle  of  the  lateral  surface  of 
the  cord  back  to  the  posterior  lateral  sulcus  as  far  do^^^l  as  the 
lumbar  cord.  Below  the  second  lumbar  segment  its  absence 
allows  the  lateral  pyramidal  tract  to  come  to  the  surface.  The 
(posterior)  cerebello-spinal  tract  runs  from  the  dorsal  nucleus 
(Clarki)  of  the  cord  to  the  superior  worm  of  the  cerebellum. 
Its  fibers  are  axones  of  vesicular  cells  in  that  nucleus.  In  the 
medulla,  it  forms  a  part  of  the  restiform  body.  It  conveys  impulses 
of  the  muscular  sense,  received,  especially,  from  the  viscera  (?). 
In  the  dorso-lateral  part  of  the  cerebello-spinal  tract  is  a  small 
strand  of  fibers  discovered  by  Horsley  and  Thiele  in  1901,  called 
the    spino-vestibular   tract.     It  rises  in  the  lumbo-sacral  region 


358  '  THE    SPINAL    CORD. 

of  the  cord  and,  ascending  along  the  surface  of  the  cerebello-spinal 
tmct  to  the  medulla,  it  winds  inward  dorsal  to  the  restiform  body 
and  terminates  in  the  nucleus  of  the  descending  root  of  the  vestib- 
ular nerve. 

The  lateral  pyramidal  tract  (fasciculus  cerebro-spinalis 
lateralis)  forms  a  considerable  part  of  the  lateral  column  of  the 
spinal  cord  (Figs.  102  and  103).  It  is  covered,  superficially,  by 
the  cerebello-spinal  tracts  in  the  cervical  and  thoracic  cord;  but 
in  the  lumbar  and  sacral  cord  it  forms  part  of  the  surface.  Its 
deep  surface  is  in  relation  with  the  posterior  columna  of  gray 
matter,  the  lateral  fasciculus  proprius  and  the  marginal  bundle. 
The  fibers  composing  it  are  axones  of  cell-bodies  in  the  anterior 
central  gyrus  of  the  cerebral  cortex.  They  rise  with  those  of  the 
anterior  pyramidal  tract,  and  the  two  run  as  one  tract  down 
through  the  genu  and  anterior  two-thirds  of  the  occipital  part 
of  the  internal  capsule,  the  middle  three-fifths  of  the  basis  pedun- 
culi,  the  anterior  longitudinal  fibers  of  the  pons  and  the  pyramid 
of  the  medulla.  In  the  medulla  the  two  tracts  separate.  The 
lateral  tract,  comprising  four-fifths  of  the  pyramid,  decussates 
with  its  fellow  through  the  anterior  median  fissure,  pierces  the 
anterior  gray  columna  and  descends  with  some  uncrossed  fibers 
in  the  lateral  column  of  the  cord.  It  terminates  in  relation  with 
the  cell-bodies  within  the  posterior  columna,  according  to  Schafer, 
Collier  and  others.  The  anterior  tract  follows  the  anterior  median 
fissure  as  already  described.  Both  end  chiefly  in  the  gray  crescent 
opposite  to  their  cortical  origin.  According  to  Marchi,  ten  or 
twenty  per  cent,  of  the  fibers  remain  uncrossed.  The  pyramidal 
tracts  are  the  cerebral  motor  tracts.  By  them  motor  and  inhibitory 
impulses  are  carried  to  the  cord.  In  the  outer  part  of  the  lateral 
pyramidal  area  is  found  the  crossed  descending  tract  of  the  red 
nucleus,  the  rubro-spinal  tract  (Pawlow). 

The  Rubrospinal  Tract  (Fig.  102).— It  extends  as  far  as  the 
first  lumbar  segment  and  ends  in  the  center  of  the  gray  crescent. 
Its  origin  in  the  nucleus  ruber,  its  crossing  through  the  ventral 
tegmental  decussation  (Foreli)  and  its  course  down  the  brain 
stem  have  been  described.  The  rubro-spinal  tract  is  descending 
in  direction.  '  ^^t^'^h'i^.^J^'^-^^ 


TRACTS    OF    THE    SPINAL    CORD.  359 

Lesions. — ^Thc  pyramidal  tracts  (especially  the  lateral)  are 
involved  in  lateral  sclerosis  and  in  amyotrophic  lateral  sclerosis; 
and,  as  a  consequence  of  it,  both  voluntary  and  inhibitor}-  impulses 
from  the  brain  are  interfered  with,  hence  the  spastic  paralysis 
and  exaggerated  reflexes.  The  pyramidal  tract  may  be  more 
or  less  involved  in  insular  sclerosis  and  in  bulbar  paralysis,  and 
the  symptoms  vary  with  the  amount  of  sclerosis.  Gliosis  of  the 
pyramidal,  cerebello-spinal  and  posterior  tracts  (Dejerine  and 
Letulle)  has  been  demonstrated  in  Friedreich's  hereditary  ataxia, 
and  the  involvement  of  the  pyramidal  tracts  explains  the  spastic 
paralysis  which  affects  both  arms  and  legs.  In  ataxic  paraplegia 
(Gowersi)  there  is  diffuse  sclerosis  of  the  lateral  and  posterior 
columns  of  the  cord.  It  is  the  degeneration  in  the  pyramidal 
tracts  that  causes  the  spastic  gait,  incoordinated  arm  movements 
and  early  increase  of  the  reflexes,  observed  in  that  affection. 

The  marginal  tract  (fasciculus  marginalis,  Lissaueri)  is  a 
small  tract  composed  of  the  ascending  branches  from  the  outer 
set  of  fibers  in  the  posterior  roots  of  the  spinal  nerves  (Figs.  102 
and  103).  It  is  situated  in  the  lateral  column  on  the  outer  surface 
and  apex  of  the  posterior  columna.  Its  fibers  are  of  small  cahber 
and,  after  ascending  a  short  distance,  end  about  the  cell-bodies 
of  the  substantia  gelatinosa. 

Tracts  of  the  Posterior  Column  of  the  Cord  (Fig.  loi). — 
In  the  posterior  column  of  the  spinal  cord,  there  are,  first,  two 
ascending  and  two  descending  tracts,  derived  from  posterior 
nerve  roots;  second,  the  posterior  fasciculus  proprius,  which  is 
much  scattered  and  is  httle  understood;  and,  third,  the  entr}'  zone 
occupied  by  the  incoming  fibers  of  the  posterior  roots. 

Entry  Zone  (Figs.  102  and  103). — Over  the  apex  and  along 
the  medial  surface  of  the  posterior  columna  of  gray  substance  the 
posterior  roots  of  the  spinal  nerves  enter  the  cord  and  divide 
T-Hke  into  ascending  and  descending  branches.  The  name 
entry  zone  is  well  applied  to  this  region.  The  presence  of  hori- 
zontal fibers  distinguishes  the  entr}-  zone  from  the  longitudinal 
tracts.  The  root-fibers  of  small  caliber  and  many  collaterals 
very  soon  enter  the  gray  substance.  The  large  fibers,  in  part, 
enter  the  dorsal  nucleus,  but  the  greater  number  form  the  longit- 


360  THE    SPINAL    CORD. 

udinal  tracts  of  the  posterior  column.  The  ascending  fibers 
begin  their  upward  course  in  the  entry  zone.  As  they  ascend  they 
are  crowded  toward  the  median  septum  by  the  entrance  of  new 
root-fibers  in  the  succeeding  upper  segments.  So  the  fibers 
near  the  septum  are  those  which  enter  low  down  in  the  cord  and 
those  close  to  the  posterior  columna  are  of  recent  entrance  into 
the  cord.  The  descending  T-branches  and  collaterals  of  the 
posterior  roots  begin  their  descent  also  in  the  entry  zone.  Some 
of  them  run  a  long  course,  even  from  the  sixth  cervical  to  the 
sacral  segments  (Collier).  The  greater  number  are  much  shorter. 
From  above  downward  they  are  crowded  in  a  dorso-medial  direc- 
tion, like  the  ascending  fibers ;  and,  after  a  considerable  downward 
course,  they  plunge  forward  through  the  white  column  to  end  in 
the  posterior  columna.  These  ascending  and  descending  fibers, 
whose  origin  is  in  the  spinal  ganglia  on  the  posterior  roots  of  the 
spinal  nerves,  together  with  the  fibers  of  the  posterior  fasciculus 
proprius  which  rise  in  the  posterior  columna,  constitute  the  longit- 
udinal tracts  of  the  posterior  column  of  the  spinal  cord.  That 
posterior  column  is  undivided  by  any  sulcus  below  the  eighth 
thoracic  segment,  where  the  posterior  intermediate  furrow  and 
septum  fade  away*  but,  above  that  level,  it  is  subdivided  into 
two  distinct  ascending  tracts,  a  postero-medial,  the  fasciculus 
gracilis,  and  a  postero-lateral,  the  fasciculus  cuneatus  (Fig.  102). 
These  two  tracts  are  alike  in  constitution.  They  have  the  same 
function,  carrying  impressions  of  the  muscular  and  tactile  senses. 
They  differ  only  in  length ;  the  fibers  of  the  fasciculus  gracilis 
come  from  the  spinal  nerves  below  the  eighth  thoracic,  while  those 
of  the  fasciculus  cuneatus  come  entirely  from  thoracic  and  cervical 
nerves. 

Fasciculus  Gracilis  (Ascending  Postero-medial  Tract,  GoU's 
Column). — ^This  tract  may  be  said  to  begin  at  the  entrance  of  the 
posterior  root  of  the  coccygeal  nerve  (Figs.  102  and  103).  It 
ascends  along  the  posterior  median  septum  to  the  nucleus  funiculi 
gracihs  of  the  medulla.  Up  to  the  lower  thoracic  nerves  it  gradu- 
ally enlarges,  due  to  the  acquisition  of  successive  posterior  root- 
fibers;  and  in  this  region,  excepting  only  the  entry  zone  and  the 
descending  branches  of  the  posterior  roots,  it  comprises  the  whole 


TRACTS    OF    THE    SPINAL    CORD.  36 1 

extrinsic  part  of  the  posterior  column.  Its  size  is  uniform  in  the 
upper  three-fourths  of  the  cord,  where  the  posterior  intermediate 
furrow  separates  it  from  the  fasciculus  cuneatus.  In  depth  it 
reaches  to  the  posterior  commissure.  Its  fibers  are  the  ascending 
branches  of  the  spinal  gangUa  cells.  Arriving  at  the  clava,  all 
the  fibers  of  the  fasciculus  graciHs  arborize  and  end  in  the  nucleus 
funiculi  gracilis. 

Fasciculus  Cuneatus  (Ascending  Postero-lateral  Tract, 
Burdach's  Column). — Beginning  in  the  lower  thoracic  segments 
(Fig.  102)  the  fasciculus  cuneatus  ascends  between  the  entry  zone 
and  the  fasciculus  graciHs  to  the  nucleus  funicuH  cuneati  of  the 
medulla.  It  acquires  new  fibers  from  every  spinal  nerve  above 
its  origin  and  grows  stronger  up  to  the  first  cervical  nerve.  In 
section  it  is  wedge-shaped,  being  broadest  at  the  surface;  the  edge 
of  the  wTdge  touches  the  junction  of  the  posterior  columna  and 
posterior  commissure.  Its  fibers  are  ascending,  and  are  branches 
of  the  axones  of  spinal  gangha  cells,  like  the  fasciculus  graciUs. 
In  the  nucleus  funicuh  cuneati  all  its  fibers  arborize  and  terminate 
(Collier). 

Descending  Tracts  Derived  from  Posterior  Roots. — ^The 
descending  fibers  from  the  posterior  roots  of  the  spinal  nerves 
arrange  themselves  somewhat  roughly  into  two  tracts,  a  postero- 
lateral and  a  postero-medial  (Figs.  102  and  103).  These  descend- 
ing radicular  tracts  greatly  expand  and  multiply  the  terminal 
relations  of  the  posterior  root-fibers.  ^Mingled  \\-ith  them,  there 
are  many  fibers  of  the  posterior  fasciculus  proprius. 

The  descending  postero-medial  tract  (Figs.  102  and  103) 
has  received  various  names  at  different  levels.  In  the  cervical 
and  upper  nine  thoracic  segments,  it  is  the  comma  tract  (of 
Schultze),  situated  in  the  fasciculus  cuneatus.  Its  ventral  part 
disappears  in  the  posterior  columna  above  the  tenth  segment, 
but  the  remainder  continues  do\\-n  the  cord.  Shifting  its  position 
in  a  dorso-medial  direction,  it  takes  its  place  beside  the  median 
septum  and  gradually  approaches  the  cord's  posterior  surface. 
It  continues  in  that  situation  to  the  end  of  the  cord,  and  is  called, 
in  succession,  the  oval  tract  (of  Flechsig),  the  septo-marginal 
tract  (of  Bruce  and  Muir),  and  the  median  triangular  tract 


362  THE    SPINAL    CORD. 

(of  Gambault  and  Phillipe).  Fibers  from  the  spinal  nerves  enter 
this  postero-medial  descending  tract  in  the  cervical,  thoracic, 
and,  at  least,  the  upper  lumbar  segments.  After  a  variable  course 
within  the  tract,  the  fibers  plunge  forward  into  the  posterior 
columna  of  gray  substance  where  they  terminate. 

The  descending  postero-lateral  tract  (Fig.  103),  situated 
at  the  posterior  surface  of  the  cord  medial  to  the  entry  zone,  in 
the  lumbo-sacral  region,  appears  to  have  been  first  described  by 
Thiele  and  Horsley.  It  is  very  largely  endogenous,  but  contains 
a  number  of  root-fibers  (Collier).  In  section  it  is  triangular. 
Its  fibers  terminate  in  the  posterior  columna  of  gray  substance. 
Both  the  descending  radicular  tracts  are  intermingled  with  endog- 
enous fibers  that  belong  to  the  fasciculus  proprius. 

Posterior  Fasciculus  Proprius.  {Fasciculus  posterior  pro- 
prius).— ^This  is  made  up  of  association  fibers  that  connect  different 
segments  of  the  cord.  It  is  not  a  compact  strand.  Its  fibers  are 
scattered  throughout  the  posterior  column,  but  they  are  especially 
numerous  in  the  descending  radicular  tracts,  in  the  region  along 
the  ventral  one-third  of  the  septum  (the  bandelette  of  Hoche) 
and  in  the  cornu  commissural  field  of  Marie  (Figs.  102  and  103). 

The  cornu  commissural  tract  (Fig.  103)  is  placed  between 
the  posterior  columna  (cornu),  the  posterior  commissure  and  the 
posterior  septum.  It  extends  up  to  the  eleventh  thoracic  segment 
and  downward  to  the  end  of  the  cord.  It  contains  both  ascending 
and  descending  fibers  as  do  other  parts  of  the  fasciculus  proprius. 

Lesions  in  the  posterior  columns  cause  disturbances  of  the 
muscular  and  tactile  senses,  and  ataxia  and  incoordination  result. 
If  the  entry  zone  is  involved  there  is  disturbance  of  all  kinds  of 
common  sensation,  at  the  level  of  the  lesion.  These  columns 
are  usually  involved,  by  extension  from  the  posterior  roots,  in 
locomotor  ataxia  (posterior  sclerosis),  hence  the  parsesthesia, 
crises,  loss  of  reflexes,  disturbed  equilibrium  and  ataxic  gait. 

ROOTS  OF  THE  SPINAL  NERVES. 

Thirty-one  pairs  of  spinal  nerves  connect  the  cord  with  the  per- 
iphery.    Each  nerve  is  joined  to  the  cord  by  two  roots:  an  ante- 


ROOTS    OF    THE    SPINAL    NERVES.  363 

rior,  ejjerent  or  motor  root  and  a  posterior,  afjerent  or  sensory  root 
(Figs.  100  and  104).  These  roots  descend  more  or  less  from  their 
cord  attachment  to  the  inter- vertebral  foramen  in  which  they 
unite  to  form  the  spinal  nerve.  The  roots  of  the  first  cervical 
nerve  are  horizontal;  those  of  the  first  thoracic  nerve  descend  the 
width  of  two  vertebrae,  and  those  of  the  twelfth  thoracic,  the  width 
of  four  vertebras;  while  the  roots  of  the  coccygeal  ner\^e  extend 
from  the  first  lumbar  vertebra  to  the  second  piece  of  the  coccyx, 
through  ten  vertebrae. 

Anterior  Root. — ^In  all  spinal  nerves,  except  the  first,  the 
anterior  root  {radix  anterior)  is  smaller  than  the  posterior.  It  is 
composed  of  from  four  to  six  fascicuH,  which  soon  combine  into 
two  bundles.  After  piercing  the  dura  mater,  the  anterior  root 
unites  with  the  posterior,  beyond  the  latter's  ganglion,  and  forms 
a  spinal  nerve.  The  anterior  root  is  efferent,  or  motor,  in  func- 
tion. 

Apparent  Origin  (Fig.  104). — ^The  anterior  root  is  composed 
of  meduUated  axones  which  issue  from  the  narrow  longitudinal 
area  at  the  junction  of  the  anterior  one-fourth  with  the  posterior 
three-fourths  of  the  cord's  surface.  This  area  is  bounded  later- 
ally by  the  anterior  root-line,  commonly  called  the  anterior  lateral 
sulcus. 

Real  Origin  (Fig.  104). — ^These  medullated  axones  rise  from 
the  medial,  lateral,  and  intermedio-lateral  columns  of  cell-bodies 
on  the  same  side  of  the  cord  and  from  the  medial  column  of  the 
opposite  side.  These  cell-bodies  of  the  anterior  columnas  and 
the  intermedio-lateral  column  constitute  the  genetic  nuclei  {nuclei 
origines)  of  the  spinal  nerves.  The  fibers  of  large  caliber  in  the 
anterior  roots  rise  from  the  cell-bodies  in  the  anterior  columnae. 
They  are  voluntary  motor  fibers.  In  the  intermedio-lateral  column, 
the  small  fibers  of  the  anterior  roots  take  their  origin.  They  are 
probably  sympathetic  in  function,  that  is,  involuntary  motor, 
vaso -motor,  viscero-motor,  inhibitory,  secretory,  trophic,  inhibito- 
secretor}',  and  inhibito-trophic. 

Lesions. — The  lower  motor  neurones  (spinal  and  cerebral) 
are  probably  in  a  state  of  toxic  irritation  in  lar}Tigismus  stridulus, 
tetanus,  acute  ascending  paralysis  (Landry),  strychnine  poisonings 


364  THE    SPINAL    CORD. 

etc.,  hence  the  twitchings,  spasms  and  convulsions.  Their  de- 
struction causes  flaccid  paralysis  (lower  segment  paralysis).  In 
spinal  meningitis  both  the  anterior  and  posterior  roots  are  affected. 

The  posterior  root  {radix  posterior)  is  the  sensory,  or  afferent 
root  (Figs.  100  and  104).  It  is  larger  than  the  anterior  root, 
except  in  the  case  of  the  first  cervical  nerve;  and  is  composed  of 
from  six  to  eight  fasciculi,  which  also  combine  at  once  into  two 
bundles.  The  posterior  root  pierces  the  dura  mater  separately 
from  the  anterior  root.  It  unites  with  the  anterior  root  in  the 
intervertebral  foramen.  Near  the  outer  end,  it  presents  a  swell- 
ing which  contains  large  vesicular  unipolar  cell-bodies  and  is  called 
a  spinal  ganglion  (ganglion  spinale).  The  ganglion  (Figs.  100 
and  128)  and  posterior  root  are  occasionally  absent  on  the  first 
nerve.  The  posterior  root,  external  to  the  ganglion,  is  made  up 
of  the  dendritic  processes  (Cajal)  of  the  ganghon  cells.  These 
dendrites,  which  in  appearance  are  axones,  extend  to  the  most 
distant  parts  of  the  body;  they  are  the  sensory  fibers  of  the  spinal 
nerves.  On  the  proximal  side  of  the  ganglion,  the  posterior  root 
is  composed  of  axones,  which  rise  from  the  ganglion  cells.  Both 
the  axonic  and  dendritic  processes  are  medullated. 

Apparent  Central  Termination  (Fig.  104). — ^The  posterior  roots 
of  the  spinal  nerves  enter  the  posterior-lateral  sulcus;  and,  at 
once,  divide  into  an  outer  set  of  small  fibers  and  an  inner  set  of 
large  fibers  with  some  small  ones  interspersed.  The  fibers  of  each 
set  bifurcate  into  a  large  ascending  and  a  smaller  descending 
branch.  Collaterals  rise  from  the  parent  axone  and  from  both 
branches. 

Real  Central  Termination,  Terminal  Nuclei  (Fig.  104). — ^The 
ascending  divisions  of  the  outer  set  of  fibers  run  a  short  distance 
along  the  external  surface  of  the  posterior  columna,  and  end  in 
ramifications  about  the  cell-bodies  of  the  substantia  gelatinosa. 
They  form  the  marginal  tract  (of  Lissauer).  Probably  their  de- 
scending branches  have  the  same  ending.  The  T-branches  and 
collaterals  of  the  inner  set  of  fibers  from  the  posterior  root  run: 
(i)  To  the  gray  matter  of  the  cord,  viz. :  To  all  parts  of  the 
posterior  columna,  to  the  center  of  the  crescent,  and  to  the  anterior 
columna  on  the  same  side,  and,  through  the  posterior  commis- 


ROOTS    OF    THE    SPINAL    NERVES.  365 

sure,  to  the  center  and  columnae  of  the  opposite  crescent.  These 
fibers  end  in  relation  with  the  dendrites  or  cell-bodies  situated  in 
those  several  regions  of  the  crescent  at  various  levels:  (a)  At  the 
same  level  as  the  nerve,  (b)  at  a  lower  level  than  the  nerve,  through 
the  descending  radicular  tracts,  and  (c)  at  a  higher  level,  through 
the  collaterals  given  off  by  the  ascending  tracts.  (2)  The  large 
ascending  T-branches  of  the  inner  set  of  libers  run  to  the  me- 
dulla oblongata.  They  form  the  fasciculus  gracihs  and  fasciculus 
cuneatus  and  ascend  to  the  nuclei  of  those  columns  in  the  medulla 
oblongata.  They  terminate  in  the  nuclei  funiculi  gracihs  and  cu- 
neati.  Hence  the  terminal  nuclei  {nn.  terminales)  of  any  spinal 
nerve  are  composed  of  the  gray  crescents  of  the  cord,  chiefly  at 
the  same  level,  and  of  the  nucleus  funiculi  gracilis  or  the  nucleus 
funiculi  cuneati  in  the  medulla. 

Physiologically,  we  may  divide  the  fibers  of  the  posterior 
roots  of  the  spinal  nerves  into  jour  groups,  viz.:  i.  Excito-reflex 
fibers  which  terminate  in  all  parts  of  both  crescents.  2.  Fibers 
bearing  impulses  of  the  muscular  and  tactile  senses  from  muscles, 
tendons,  joints  and  skin,  through  the  posterior  column,  to  the  nu- 
cleus funicuh  gracilis  and  nucleus  funiculi  cuneati.  3.  Fibers 
carrying  impulses  of  the  muscular  sense  from  the  viscera  to  the 
dorsal  nucleus.  4.  Fibers  transmitting  pain,  temperature  and 
tactile  impulses  to  that  part  of  the  same  and  opposite  crescent 
whence  the  spino-thalamic  and  ascending  anterior  cerebello-spinal 
tracts  take  their  origin. 

Lesions. — ^The  posterior  roots  of  the  spinal  nerves  and  the  spinal 
gangha  are  affected  in  locomotor  ataxia,  and  the  lesion  extends 
to  the  marginal  tract  (of  Lissauer)  and  the  posterior  column  of  the 
cord.  Excepting  the  fasciculus  proprius,  the  whole  posterior 
column  becomes  involved. 


CHAPTER  VII. 

TRACING  OF  IMPULSES. 

Having  studied  the  grouping  and  chaining  together  of  neu- 
rones, let  us  now  make  the  knowledge  practical  by  tracing  impul- 
ses through  the  better  known  paths  formed  by  these  various  neu- 
rone groups.  The  paths  thus  formed  are  of  three  kinds,  namely: 
I.  Efferent,  or  motor.  II.  Afferent,  or  sensory — general  and  spe- 
cial sense.     III.  Reflex. 

I.  EFFERENT,  OR  MOTOR  PATHS. 

The  CEREBRO-SPINAL  OR  PYRAMIDAL  PATHS  (Fig.  105) 
are  direct,  as  they  do  not  pass  through  the  cerebellum.  Their  im- 
pulses ultimately  run  either  through  the  spinal  or  the  cerebral  nerves, 
and  are  both  motor  and  inhibitory.  Hence  the  increased  reflexes 
and  spastic  contractions  of  lateral  sclerosis  in  which  these  tracts 
are  diseased. 

I,  Through  th'e  Spinal  Nerves  (Fig.  105). — Starting  in  the 
upper  three-fourths  of  the  gyrus  centraHs  anterior  of  the  cerebral 
cortex,  motor  and  inhibitory  impulses  run  down  through  the  corona 
radiata,  the  anterior  two-thirds  of  the  occipital  part  of  the  inter- 
nal capsule,  the  middle  three-fifths  of  the  basis  pedunculi,  the 
anterior  longitudinal  fibers  of  the  pons,  and  the  pyramid  of  the 
medulla  oblongata,  whence  they  proceed  by  the  lateral  and  an- 
terior pyramidal  tracts  to  the  gray  crescent,  partly  in  the  same  side 
but  chiefly  in  the  opposite  side  of  the  spinal  cord.  By  the  former 
route,  the  impulses  cross  over  in  the  medulla,  through  the  decus- 
sation of  the  pyramids,  and  descend  in  the  lateral  column  of  the 
spinal  cord  to  the  gray  substance  in  the  vicinity  of  the  nucleus 
dorsalis  (Clarki),  where  the  path  is  relayed,  and  intrinsic  neurones 
carry  the  impulses  forward  into  the  anterior  columna;  but  by  the 
anterior  route,  they  descend  in  the  anterior  column  of  the  cord 
and  decussate,  in  succession,  through  the  white  anterior  com- 

366 


EFFERENT,  OR  MOTOR  PATHS. 


367 


Accessary  fillet  (Bechterewi) 
to  nuclei  of  cerelDral  nerves 


eus  pontis 


Medull 


Anterior 
Pj'ramidal  tract 


Pyramid 


Pyramidal  decussation 

Lateral  pyramidal 
tract 


Cord 


Anterior  root  of  spinal  nerve 

Fig-   105.— Direct  motor  paths  from  cerebral  cortex,  to  cerebral  and  spinal  nerves. 
Diagrammatic.    {Original.) 

Motor  paths  extending  from  the  corte.x  of  the  anterior  central  gyvns  to  the  nuclei  of  the 
motor  cerebral  nerves  and  of  the  anterior  roots  of  the  spinal  nerves;  ®.  represents  point 
where  the  section  is  pierced  by  a  longitudinal  fiber;  3,  4,  5,  6,  7,  9,  10,  11,  and  12,  nuclei  of 
cerebral  nerves. 


EFFERENT,    OR    MOTOR    PATHS.  369 

missurc.  Impulses  by  either  route  finally  reach  the  anterior  gray 
columna  of  the  spinal  cord  and,  with  the  exception  of  a  small 
per  cent,  of  them,  they  reach  the  columna  opposite  to  their  cortical 
origin.  The  few  undecussated  fibers  in  the  lateral  pyramidal 
tract  conduct  uncrossed  impulses  to  the  anterior  columna  of  the 
same  side.  Thus  are  explained  two  symptoms  of  hemiplegia 
due  to  cerebral  lesion,  viz.,  weakness  on  the  well  side  and  slight 
motion  on  the  paralyzed  side.  From  the  anterior  gray  columna 
of  the  spinal  cord  the  nerve  commotions  are  conducted  by  the 
efferent,  or  motor  fibers  of  the  spinal  nerves  to  the  muscles. 

2.  Through  the  Cerebral  Nerves  (Fig.  105). — ^Impulses  des- 
tined to  the  cerebral  nerves  run  chiefly  from  the  lower  two-fourths 
of  the  anterior  central  gyrus  through  corona  radiata,  genu  of  in- 
ternal capsule  and  on,  by  the  same  path  as  the  impulses  to  spinal 
nerves,  down  to  the  point  where  they  leave  the  pyramidal  tract 
to  enter  the  nuclei  of  the  cerebral  nerves,  which  some  of  them  do 
in  the  vicinity  of  the  several  nuclei.  According  to  Bechterew^ 
they  run,  at  least  in  part,  through  pyramidal  fibers  which  consti- 
tute the  accessory  lemniscus.  These  fibers  leave  the  pyramidal 
tract,  near  the  internal  capsule,  and  descend  through  the  medial 
portion  of  the  fillet  to  points  near  the  respective  nuclei  in  which 
they  end  by  multiple  division.  From  either  hemisphere  impul- 
ses proceed  to  the  nuclei  of  both  sides.  But  the  greater  number 
enter  the  nucleus  of  the  fourth  nerve  on  the  same  side,  and  the 
nuclei  of  the  third,  fifth,  sixth,  seventh,  ninth,  tenth,  eleventh 
and  twelfth  cerebral  nerves  of  the  opposite  side.  By  the  above 
nine  nerves  innervation  is  conducted  to  the  muscles  of  the 
orbit ;  the  muscles  of  mastication,  and  expression ;  the  muscles 
of  the  tongue,  palate  and  ear;  the  digastric  and  styloid  muscles; 
the  muscles  of  the  larynx,  trachea  and  bronchi,  and  of  the  pharynx, 
esophagus,  stomach,  and  the  intestines  down  to  the  descending 
colon.  And  inhibitory  impulses  are  carried  to  the  heart;  also 
vasodilator,  secretory,  trophic  and  inhibito-secretory  impulses 
to  alimentary  glands,  etc. 

THE   CEREBRO-PONTAL  PATHS,  FRONTAL,  TEMPO- 
RAL AND  INTERMEDLATE.— These   paths  arc  indirect,  for 
spinal  nerves,  since  they  run  through  the  cerebellum. 
24 


370  TRACING    OF    IMPULSES. 

Fronto-pontal  (Fig.  io6). — ^The  impulses  originate  in  the 
frontal  region  (?),  and  descend  through  corona  radiata,  the 
frontal  part  of  the  internal  capsule,  and  the  medial  fifth  of  the 
basis  peduncuH  to  the  nucleus  pontis.  Temporo-pontal. — ^They 
rise  in  the  temporal  cortex  and  run  through  corona  radiata,  the 
occipital  part  and  inferior  lamina  of  the  internal  capsule,  and  the 
lateral  fifth  of  the  basis  peduncli  to  the  nucleus  pontis.  Both 
the  fronto-pontal  and  the  temporo-pontal  paths  are  probably 
relayed  in  the  corpus  striatum  or  the  thalamus.  Intermediate 
Bundle. — Cortical  impulses  of  unknown  origin  are  received  by 
the  corpus  striatum  and  conveyed,  by  a  bundle  of  centrifugal 
axones  which  form  the  deep  portion  of  the  basis  peduncuH,  to  the 
substantia  nigra  and  then  to  the  nucleus  pontis,  chiefly  of  the 
same  side.  The  impulses  thus  traverse  the  internal  capsule  and  a 
broad  but  thin  area  in  the  basis  pedunculi  just  ventral  to  the  sub- 
stantia nigra  and  dorsal  to  the  pyramidal  tract.  In  all  three  of 
these  paths  the  impulses  run  to  the  nucleus  pontis  of  the  same 
side  and  to  motor  nuclei  of  the  cerebral  nerves.  Whence  they 
proceed  from  nucleus  pontis:  (i)  To  Spinal  Nerves.  They  run 
through  the  brachium  pontis  to  the  cerebellar  cortex  and,  thence, 
continue  down  the  anterior  descending  cerebello-spinal  tract  to 
the  anterior  gray  columna  of  the  spinal  cord.  Their  course  from 
the  cerebellar  cortex  is  through  the  acustico-cerebellar  tract  and 
the  restiform  body,  the  lateral  area  of  the  medulla  and  the  antero- 
lateral column  of  the  cord.  From  the  gray  matter  of  the  spinal 
cord  the  impulses  are  conveyed  by  the  motor  fibers  of  the  spinal 
nerves  to  the  muscles  which  they  supply.  {2)  To  Cerebral  Nerves. 
The  impulses  run  from  the  S3rnapses  formed  in  the  cerebral  nuclei, 
by  the  fibers  of  the  cerebro-pontal  tracts,  through  the  motor 
fibers  of  these  nerves  to  their  distribution. 

PATHS  THROUGH  THE  RED  NUCLEUS  (Fig.  106).— 
There  are  two,  a  direct  and  an  indirect.  Impulses  run  from  some 
part  of  the  cerebral  cortex  to  the  thalamus  and  red  nucleus  or  to 
the  corpus  striatum  and  red  nucleus.  From  the  red  nucleus 
they  pursue  either  a  direct  or  indirect  route. 

(i)  Direct  Route,  The  Rubro-spinal  Path. — ^By  the  direct 
route,  impulses  run  through  the  crossed  descending  tract  of  the 


EFFERENT,  OR  MOTOR  PATHS. 


zn 


Fibers  from  red  nucleus 
to  .nucleus  dentatus 


Temporo-pontal  tract 
Intermediate  tract 
Fronto-Pontal  tract 


Nucleus  pontis  containing  end- 
ings of  cerebro-pontal  tracts 
«  and  origin  of.brachium  tontisl 
DescendilTg  ant.  cerebello- 
spinal tract 


Rubro-spinal  tract 


Anterior  root  of  spinal  nerve 


Fig.  io6. — Indirect  motor  paths  to  the  spinal  nerves.     Diagrammatic.  (Original.) 

Motor  paths  from  cerebral  cortex  through  the  cerebellum  to  spinal  nerves.  A.  Fronto- 
pontal  tract  rising  in  frontal  lobe.  B.  Intermediate  tract  rising  in  lentiform  nucleus.  C.  Tem- 
poro-pontal tract  rising  in  middle  and  inferior  temporal  gyri.  Also  rubro-spinal  tract. 
(•)  (•)  represent  points  of  perforation  in  the  sections. 


EFFERENT,    OR    MOTOR    PATHS.  373 

red  nucleus  to  the  center  of  the  gray  crescent  in  the  opposite  side 
of  the  spinal  cord.  Crossing  the  median  raphe  at  once,  in  the 
hypothalamic  region  through  the  ventral  tegmental  decussation, 
(Foreli),  the  impulses  descend  by  way  of  the  rubro-spinal  tract, 
through  the  ventral  part  of  the  formatio  reticularis  of  the  mid- 
brain and  pons,  in  the  medial  part  of  the  lateral  fillet,  then  through 
the  lateral  area  of  the  medulla,  among  the  fibers  of  the  anterior 
ascending  cerebello-spinal  tract,  and  finally  down  the  spinal  cord, 
through  the  ventral  portion  of  the  lateral  pyramidal  area,  to  their 
destination  in  the  gray  matter.  From  the  center  of  the  gray  cres- 
cent they  proceed  with  or  vdthout  transferring  to  the  roots  of  the 
spinal  nerves,  and  are  conducted  to  the  muscles. 

(2)  Indirect  Route. — ^Impulses  from  the  red  nucleus  may  also 
run  through  the  brachium  conjunctivum,  chiefly  the  opposite 
one,  to  the  nucleus  dentatus;  and  thence,  by  axones  from  that 
nucleus,  down  the  anterior  descending  cerebello-spinal  tract, 
which  continues  their  path  to  the  columna  anterior  of  the  cord. 

PONTO-SPmAL  PATHS.— The  ponto-spinal  tract  is  the 
name  suggested  by  Collier  for  the  tracts  originating  in  the  nuclei 
of  the  reticular  formation,  chiefly  in  the  pons,  and  descending 
to  the  gray  matter  of  the  spinal  cord.  There  are  two  of  them  on 
either  side.  The  medial  ponto-spinal  tract  accompanies  the 
medial  longitudinal  bundle  down  the  anterior  ground  bundle  of 
the  cord  without  decussating,  unless  the  crossing  occurs  near  the 
termination.  The  lateral  ponto-spinal  tract,  which  is  crossed, 
decussates  in  the  brain  stem  near  its  origins  and  descends  in  the 
lateral  column  of  the  spinal  cord.  Just  how  the  impulses  reach 
the  nuclei  centrales  and  nuclei  laterales  of  the  formatio  reticularis, 
in  which  the  ponto-spinal  tracts  take  their  origins,  cannot  be 
definitely  stated;  but,  having  arrived  in  them,  they  descend  to 
both  crescents  of  the  spinal  cord  and  apparently  enter  into  all 
its  segments.     The  anterior  nerve  roots  complete  the  paths. 

Short  Fiber  Paths. — ^Those  are  paths  in  the  formatio  reticula- 
ris chiefly,  (i)  Impulses  having  reached  the  great  ganglia  of 
the  cerebrum  and  mid-brain  may  run  through  many  relays  do\NTi 
the  formatio  reticularis  of  mid-brain,  pons  and  medulla  and  the 
antero-lateral  fasciculus  proprius  of  the  spinal  cord,  to  the  gray 


374  TRACING    OF    IMPULSES. 

crescent  of  the  same,  and  continue  through  the  anterior  root-fibers 
to  their  destination.  On  the  other  hand,  the  impulses,  leaving 
formatio  reticularis  in  mid-brain,  pons  or  medulla,  may  enter 
the  nuclei  of  motor  cerebral  nerves  and  be  conducted  by  them  to 
the  muscles  and  glands  supplied  by  cerebral  nerves.  (2)  The 
impulses  may  leave  the  formatio  reticularis  in  the  pons,  and  run 
to  the  cerebellar  cortex  through  the  brachium  pontis.  From  the 
cerebellum  they  may  follow  the  ordinary  course  through  the  an- 
terior descending  cerebello-spinal  tract,  by.  way  of  the  nucleus 
of  Deiters,  to  the  anterior  gray  columna  of  the  cord.  (3)  Impul- 
ses having  arrived  at  the  cerebellar  cortex  by  way  of  the  brachia 
conjunctiva  and  brachia  pontis,  may  descend  through  the  cere- 
bello-olivary  tract,  in  the  restiform  body,  to  the  opposite  inferior 
olive,  and  be  carried  on  through  descending  axones  of  the  olive, 
in  the  lateral  column,  to  the  gray  matter  of  the  cord  (Kolliker). 
(4)  Impulses  descend  from  the  nucleus  of  the  third  cerebral  nerve 
by  way  of  certain  fibers  in  the  medial  longitudinal  bundle  to  the 
seventh  nerve,  where  it  enters  into  the  colliculus  facialis,  and 
through  the  facial  nerve  innervate  the  following  muscles — the 
frontalis,  procerus,  corrugator  and  orbicularis  oculi.  Hence  these 
muscles  are  not  paralyzed  in  nuclear  facial  paralysis.  But  if  the 
lesion  be  in  the  colliculus  fascialis  or  distal  to  it,  then  facial  paral- 
ysis is  complete.  (5)  At  the  same  eminence,  impulses  pass  into 
the  facial  nerve  from  the  hypoglossal  nucleus  via  a  small  strand 
of  axones  which  rises  in  the  hypoglossal  nucleus  and  runs  through 
the  medial  longitudinal  bundle  into  the  facial  at  the  genu  (?). 
These  impulses  innervate  the  orbicularis  oris.  (6)  Through 
certain  short  fibers  in  the  medial  longitudinal  bundle  which  rise 
in  the  nucleus  of  the  sixth  cerebral  nerve  and  cross  to  the  opposite 
nucleus  of  the  motor  oculi,  impulses  run  from  the  nucleus  of  the 
abducent  through  the  opposite  third  nerve  to  the  internal  rectus 
oculi.  They  explain  the  conjugate  action  of  the  eyes  in  health, 
and  also  the  conjugate  deviation  observed  in  lesions  affecting  the 
nucleus  of  the  sixth  nerve.  In  nuclear  lesions  of  the  abducent 
nerve  the  external  rectus  of  the  same  eye  and  the  internal  rectus 
of  the  other  eye  are  paralyzed  if  the  nucleus  is  destroyed  and 
stimulated  if  the  nucleus  is  only  irritated. 


AFFERENT,  OR  SENSORY  PATHS. 


375 


D3cussation  ofjbrachia  conjunctiva 
Brachium,  conjunctivum 


Vestibular  root 
Vlllinerve 


IX  nerve 


X  nerve 

Anterior  external  arcuate  fiber 


(Post.)  Cerebello-spinal  tract 
Fasciculus  cuneatus 
Fasciculus  gracil 


Sacral  nerve 
Cervical  nerve 
Thoracic  nerve 


Pons  and  cerebellum 


Restiform  body  containing 
arcuate  and  posterior  cerebello- 
spinal fibers 
Medial  fillet 

Nucleus  funiculi  gracilis 
Nucleus  funiculi  cuneati 


Post,  roots 
Spinal  nerves 


Fig.   107. — Common  sensory  paths,  muscular  and  tactile,  by  \vay[of  the  posterior 
column  and  (posterior)  cerebello-spinal  tract.     Diagrammatic.    ](Origi>Ml.) 

These  paths  terminate  in  the  posterior  central  gyrus  and  in  the  middle  and  inferior  tem- 
poral gi'ri. 


AFFERENT,  OR  SENSORY  PATHS.  377 

II.     AFFERENT,  OR  SENSORY  PATHS. 

The  sensory  paths  conduct  two  varieties  of  impulses,  viz., 
general  and  special.  The  impulses  originate  in  the  end-organs 
of  the  cerebral  and  spinal  nerves,  and  by  those  nerves  are  con- 
veyed to  the  cerebro-spinal  axis,  through  which  they  reach  the 
proper  cortical  area  in  the  cerebrum. 

I.  General  Sensations. 

General  sensation  is  the  function  of  the  sense  of  touch.  This 
sense  has  four  important  subdivisions — the  tactile  sense,  mus- 
cular sense,  pain  sense,  and  temperature  sense.  Stereognosis  is 
only  an  associated  interpretation  of  all  the  impulses  of  the  sense 
of  touch  and  not  a  subdivision  of  it.  Tactile  sensations  appear 
to  be  most  elemental  and,  according  to  Spiller  and  Mills,  may  be 
conducted  by  all  common  sensory  nerve  fibers.  Other  common 
sensations  seem  to  require  some  specialization,  as  yet  not  imder- 
stood,  in  their  conducting  media;  and  pain  and  temperature  im- 
pulses pursue  a  path  entirely  distinct  from  that  followed  by  im- 
pressions of  the  muscular  sense.  In  giving  the  common  sensory 
tracings,  the  following  classification  will  be  adhered  to,  though 
conclusive  e\ddence  of  certain  points  in  it  is  still  lacking. 

I.  Paths  conducting  impulses  of  the  muscular  and  tactile 
senses,  chiefly,  from  muscles,  tendons,  joint  surfaces,  and  the 
skin.     Spinal  and  cerebral  (Fig.   107). 

II.  Paths  carrying  impulses  of  the  muscular  and  tactile  sen- 
ses, chiefly  from  viscera  (?)  (Fig.  107). 

III.  Paths  conveying  pain,  temperature,  and  tactile  impulses. 
Spinal  and  cerebral  (Fig.  io8). 

I.  PATHS  TRANSMITTING  IMPULSES  OF  THE  MUS- 
CULAR AND  TACTILE  SENSES,  chiefly,  from  muscles,  tendons, 
ligaments,  joint  surfaces  and  the  skin. 

Through  Posterior  Column  and  Fasciculi  Gracilis  et  Cu- 
neatus  (Fig.  107). — Impulses  originating  in  the  end-organs  of  the 
spinal  nerves  traverse  the  dendrites  of  the  spinal  ganglion  neurones 
(Cajal),  the  cell-bodies  in  the  ganglia,  and  then  the  axones  of  the 
same.     They  enter  the  cord  through  the  posterior  roots  of  the 


378  TRACING    OF    IMPULSES. 

spinal  nerves,  and  ascend  through  the  posterior  column  as  far 
as  the  eighth  thoracic  segment  and  then  through  the  fasciculus 
gracilis,  or,  entering  above  the  eighth  thoracic  segment,  they 
ascend  through  the  fasciculus  cuneatus.  In  either  case  they  arrive 
in  one  of  the  nuclei  of  the  posterior  column,  namely,  the  nucleus 
funicuH  gracilis  or  the  nucleus  funiculi  cuneati.  Thence  the  im- 
pulses may  proceed  either  by  a  direct  or  by  an  indirect  route. 

(i)  The  direct  route  carries  the  impulses  by  way  of  the  medial 
fillet  through  the  sensory  decussation  of  the  medulla,  the  formatio 
reticularis  of  pons  and  mid-brain,  to  the  lateral  nucleus  of  the 
thalamus,  from  which  they  are  conducted  by  the  cortical  fillet 
to  the  somassthetic  area  of  the  cerebral  cortex.  In  their  last 
stage  the  impulses  run  from  the  thalamus  through  the  internal 
capsule  and  corona  radiata  to  the  posterior  central  gyrus  in  the 
equatorial  zone  of  the  hemisphere. 

(2)  Indirect  Route. — ^By  that  route  impulses  from  the  nucleus 
funiculi  gracilis  and  nucleus  funiculi  cuneati  run  to  the  cortex 
of  the  vermis  cerebelli  superior  through  the  extemaLarcuate  fibers; 
then  on,  through  the  brachium  conjunctivum,  to  the  red  nucleus 
and  thalamus.  They  traverse  the  restiform  body  of  the  same 
side,  by  way  of  the  posterior  external  arcuate  fibers;  or,  by  way 
of  the  anterior  external  arcuate  fibers,  they  traverse  the  fillet 
decussation  of  the  medulla  and  the  opposite  restiform  body  to 
reach  the  vermis  cerebelli  superior.  From  the  cerebellar  cortex, 
the  impulses  continue  through  cortical  axones  to  the  nucleus 
dentatus,  whose  axones  conduct  them  to  the  red  nucleus  and 
thalamus  of  the  opposite  side.  The  greater  number,  therefore, 
cross  over  in  the  tegmentum  of  the  mid-brain.  Their  course 
from  the  red  nucleus  and  thalamus  is  through  the  cortical  fillet 
to  the  cortex. 

These  impulses  from  the  spinal  nerves  go  to  the  upper  two- 
thirds  of  the  posterior  central  gyrus,  those  from  the  lower  extrem- 
ity to  the  upper  third  and  those  from  the  arms  to  the  middle 
third  (Spiller). 

Through  Cerebral  Nerves  and  Medial  Fillet  (Fig.  107). — 
As  crossed  fibers  from  the  terminal  nuclei  of  the  trigeminal,  the 
vestibular,  the  glossopharyngeal  and  the  vagus  nerves  join  the 


•AFFERENT,    OR    SENSORY    PATHS. 


379 


Brachium  conjunctivum 
Pons  and  cerebellum   /L^., 


Tract  from  inferior  lateral 
nucleus  to  cerebellum  via  the 
restif  orm  body- 


Medulla 


Angle  in  ascend,  ant. 
Cerebello-spinal^tract 


Gowers's 
Tract 


V  nerve 


IX  nerve 


X  nerve 


Spino-thalamic  tract 
Ascending  ant.  cere- 
'  [bello-spinal  tract 


Spinal  nerves 


Fig.  io8. — Common  sensory  paths,  pain,  temperature  and  touch,  by  way  of  ascending 
anterior  cerebello-spinal  and  spino-thalamic  tracts.    Diagrammatic.    [Original.) 

Posterior  root-fibers  connected  with  this  path  end  in  the  center  of  the  crescent  and  in  the 
base  of  the  anterior  columna  of  both  sides;  and  the  ascending  fibers  rise  partly  on  the  same 
and  partly  on  the  opposite  side ;  the  crossed  fibers  run  through  the  white  anterior  commissure. 


AFFERENT,  OR  SENSORY  PATHS.  38 1 

medial  fillet  and  run  to  the  thalamus,  so  muscular  and  tactile 
sensations  transmitted  by  those  cerebral  nerves  to  their  nuclei 
in  the  medulla  and  pons,  are  carried  by  the  medial  fillet  to  the 
lateral  nucleus  of  the  thalamus  on  the  opposite  side.  The  cortical 
fillet  conducts  them  to  the  lower  portion  of  the  posterior  central 
gyrus  in  the  somajslhetic  area. 

II.  PATHS  CARRYING  IMPULSES  OF  THE  MUSCULAR 
AND  TACTILE  SENSES,  CHIEFLY  FROM  VISCERA  (?). 

Through  (Posterior)  Cerebello-spinal  Tract  (Direct  Cere- 
bellar) (Fig.  107). — ^The  column  of  cell-bodies,  forming  the  nucleus 
dorsalis  (Clarki),  receives  impulses  concerning  equilibrium  (?) 
from  the  posterior  roots  of  the  spinal  nersTs  and  transmits  them 
at  once  to  the  (posterior)  cerebello-spinal  tract,  through  which 
they  ascend  along  the  dorso-lateral  surface  of  the  cord,  along  the 
posterior  surface  and  through  the  restiform  body  of  the  medulla 
to  the  cortex  of  the  superior  worm  of  the  cerebellum.  To  a 
small  extent  they  cross  in  the  worm  to  the  opposite  side.  These 
impulses  probably  excite,  within  the  cerebellar  cortex,  impulses 
of  coordination  and  equilibrium  which  traverse  the  descending 
anterior  cerebello-spinal  tract  to  the  gray  crescent  of  the  cord, 
and  are  transmitted  to  the  motor  neurones  of  the  anterior  columna. 
The  motor  neurones  conduct  the  impulses  to  the  muscles.  From 
the  cerebellar  cortex  the  journey  to  the  cerebrum  is  completed  in 
four  stages,  as  already  described,  namely:  Nucleus  dentatus, 
opposite  red  nucleus,  thalamus  and  some  part  of  the  cerebral 
cortex,  probably  the  middle  and  inferior  temporal  gyri. 

Probably  the  vagus  nerve  conducts  impulses  of  similar  nature 
from  the  viscera  to  its  terminal  nucleus;  but,  if  so,  their  path 
from  the  terminal  nucleus  is  not  certainly  kno\^^l. 

PATHS  CONVEYING  PAIN,  TEMPERATURE  AND  TAC- 
TILE IMPRESSIONS.     SPINAL  AND  CEREBRAL. 

Through  Spino-thalamic  and  Ascending  Anterior  Cere- 
bello-spinal Tract  (Fig.  io8). — In  the  spinal  cord,  medulla  and 
pons  these  constitute  one  tract,  commonly  called  Gowers's  tract. 
They  separate  just  below  the  isthmus,  whence  the  spino-thalamic 
tract  continues  to  the  thalamus  and  the  other  turns  back  to  the 
cerebellum.     They  appear  to  form  the  only  paths  for  pain  and 


382  TRACING    OF    IMPLTLSES. 

temperature  impulses.  These  impulses  enter  the  gray  crescent 
of  the  cord,  on  both  sides,  through  the  posterior  nerve  roots.  A 
large  number  decussate  via  the  posterior  nerve  roots  in  the  gray 
commissure;  the  rest  decussate  in  the  first  stage  of  the  ascending 
tracts,  crossing  in  the  white  anterior  commissure,  and  run  upward 
through  the  spino-thalamic  and  ascending  anterior  cerebello- 
spinal tracts  of  the  opposite  side ;  they  run  to  the  thalamus  and  to 
the  cortex  of  the  superior  worm  of  the  cerebellum.  In  the  cord  they 
ascend  along  the  lateral  surface.  They  run  dorsal  to  the  olive  in 
the  lateral  area  of  the  medulla  oblongata,  and  through  the  lateral 
part  of  the  formatio  reticularis  of  the  pons  to  the  angle  in  Gowers's 
tract  situated  near  the  isthmus.  From  the  angle,  just  below  the 
quadrigeminal  bodies,  the  cerebellar  impulses  run  backward  with 
the  tract  through  the  superior  medullary  velum  to  the  cortex  of 
the  vermis  cerebelli  superior;  the  remainder  run  upward  to  the 
thalamus,  and  from  that  to  the  posterior  central  cortex.  The 
common  course  of  sensory  impulses  from  the  cerebellar  to  the 
cerebral  cortex  is,  as  already  described,  through  nucleus  dentatus 
and  brachium  conjunctivum  to  opposite  red  nucleus  and  thala- 
mus. Having  arrived  in  the  thalamus,  they  proceed  thence  by 
the  cortical  fillet  to  the  somaesthetic  cortex. 

Certain  fibers  of  the  ascending  anterior  cerebello-spinal  tract 
diverge  from  the  others,  in  the  medulla  oblongata,  and  terminate 
in  the  inferior  lateral  nucleus.  Impulses  of  pain  and  temperature, 
following  the  same  course,  enter  the  lateral  nucleus,  and  are  carried 
on  through  the  restiform  body  to  the  cerebellum  by  the  tract 
from  the  lateral  nucleus  to  the  cerebellar  cortex,  thence  to  the 
somsesthetic  area  as  previously  given. 

Through  Cerebral  Nerves  and  the  Spino-thalamic  Tract 
(Fig.  108). — ^Pain  and  temperature  impulses  are  transmitted  by 
certain  fibers  of  the  vagus,  glossopharyngeal  and  trigeminal  nerves 
to  their  terminal  nuclei.  From  those  nuclei  they  are  conducted 
by  axones  which  probably  enter  into  the  spino-thalamic  tract, 
and,  perhaps,  into  the  ascending  anterior  cerebello-spinal  tract, 
to  the  thalamus  and  to  the  cerebellar  cortex.  The  path  from 
either  point  to  the  posterior  central  gyrus  is  now  famiUar. 

The  Short  Fiber  Paths.— What  special  varieties  of  common 


AFFERENT,  OR  SENSORY  PATHS.  383 

sensation  are  conducted  through  these  ])uths  is  unknown.  Under 
certain  conditions,  perhaps,  they  may  carry  all  varieties,  (i)  The 
antero-lateral  fasciculus  proprius  and  formatio  reticularis  contain 
ascending  axones  which  may  convey  sensory  impulses  from  the 
gray  matter  of  the  cord,  received  from  the  posterior  roots  of  the 
spinal  nerves,  and  from  terminal  nuclei  in  medulla  and  pons 
which  receive  the  common  sensory  fibers  of  cerebral  nerves,  up- 
ward to  the  thalamus  of  the  opposite  side.  The  course  from  the 
thalamus  is  by  way  of  the  cortical  fillet.  (2)  Again,  impulses 
may  leave  the  formatio  reticularis  in  the  pons  and  run  through  the 
brachium  pontis  cerebelh,  by  way  of  axones  from  the  nuclei  pon- 
tis,  to  the  cortex  of  the  cerebellum;  and  then  continue  by  the  or- 
dinary course  through  the  brachium  conjunctivum  to  the  red 
nucleus  and  thalamus. 

Destruction  of  any  of  the  above  sensory  paths  causes  diminu- 
tion or  loss  of  the  especial  variety  of  impulse  which  travels  that 
path.  Destruction  of  the  posterior  white  columns  produces 
loss  of  muscular  sensations  and  gives  rise  to  ataxia.  Interrup- 
tion of  Gowers's  tract  (spino-thalamic  and  ascending  anterior 
cerebello-spinal  tracts)  abolishes  pain  and  temperature  sensations 
while  touch  is  not  much  affected. 

2.  Special  Sensations. 

Impulses  producing  the  sensations  of  smell,  sight,  hearing 
and  taste  are  carried  from  the  respective  organs  of  sense  to  the 
brain  by  the  following  nerves:  The  olfactory;  the  optic;  the 
auditory;   and    the    glossophar3TLgeal    and    intermediate    nerves. 

Olfactory  Path  (Figs.  109  and  21). — ^Impulses  of  smell  orig- 
inate in  the  upper  third  of  the  nasal  mucous  membrane.  They 
run  through  the  olfactory  nerves  to  the  second  layer  in  the  bulb, 
where  they  are  transferred  to  the  dendrites  of  the  mitral  and  brush 
cells.  By  the  axones  of  these  cells  they  are  carried  backward 
through  the  olfactory  tract  and  striie  to  the  cerebral  hemisphere. 
The  medial  stria  conducts  them  to  the  parolfactory  area  (Brocae), 
the  triangle,  the  gyrus  subcallosus  and  anterior  end  of  the  gyrus 
cinguli,  whence,  through  the  cingulum,  the  fornix  and  uncinate 
fasciculus  thev  may  reach  the  cortical  area  of  smell  in  the  uncus 


384 


TRACING    OF    IMPULSES. 


hippocampi.  By  the  intermediate  olfactory  stria  the  impulses 
enter  the  triangle  and  anterior  perforated  substance,  and  com- 
plete their  journey  either  in  the  same  manner  as  given  above  or 
via  the  anterior  commissure.  The  lateral  stria  of  the  olfactory 
tract  conducts  the  impulses  directly  to  the  uncus  of  the  hippocam- 


Ceiitral  core  of 
ependymal  cells 


Fibers  to  0\. 
tract. 

5.   S.  granulosum 


4.  S.  cellulare 
3.  S.  reticulare 


2.  S.  glomeru- 
losum 


I.  S.  nervosum 


Nasal  mucous 
membrane 


Olfactory  cell- 
bodies 


Fig.  109. — Chief  elements  of  the  olfactory  bulb.     {Gordinier  after  Van  Gehuchten.) 

pal  gyrus.     Note  that  olfactory  impulses  are  chiefly,  if  not  entirely, 
uncrossed. 

Optic  Path  (Figs,  no  and  1 11).— Impulses  of  sight  originate 
in  the  rods  and  cones  of  the  retinae  and  traverse  three  or  more 
series  of  neurones  to  the  terminal  nuclei  of  the  optic  tracts ;  namely, 
the  rod  and  cone,  the  bipolar,  and  the  ganghonar  neurones. 
The  axones  of  the  last  form  the  optic  nerves  and  the  visual  part 


AFFERENT,  OR  SENSORY  PATHS.  385 

of  the  optic  tracts.  From  the  right  halves  of  both  retinae  and 
from  the  left  halves  of  both,  impulses  run  through  the  correspond- 
ing tract  to  the  lateral  geniculate  body  and  the  pulvinar  of  the 
thalamus;  also  to  the  superior  quadrigeminal  colliculus.  The 
latter  produces  ocular  and  pupillary  reflexes.  From  the  lateral 
geniculate  body  and  pulvinar  the  occipito-thalamic  radiation 
carries  the  impulses  through  the  pars  occipitalis  of  the  internal 
capsule  to  the  half-visual  center  in  the  cuneus,  gyrus  lingualis 
and  the  pole  of  the  occipital  lobe.  Impulses  from  the  nasal  halves 
of  the  retinas  decussate  in  the  optic  commissure;  those  from  the 


Fig.   110. — The  chief  retinal  elements.     (After  Brubaker.) 

Cells,  s'  z' .  Visual  cells  with  their  peripheral  terminations.    5.  Rods.     z.  Cones,     h.  Bipolar 
cells,     g.  Ganglion  cells  from  which  arise  the  axones  of  the  optic  nerve. 

temporal  halves,  for  the  most  part  at  least,  remain  on  the  same 
side,  but  a  few  may  cross  through  the  quadrigeminal  coUiculi 
and  brachia  superiora.  Impulses  from  the  nasal  half  and  from 
the  temporal  half  of  the  macula  lutea  are  conducted  equally  by 
both  optic  tracts.  Hence  destruction  of  one  tract  causes  hem- 
ianopsia, preserving  the  vision  in  the  corresponding  half  of  each 
visual  field,  and  also  diminishes  the  acuteness  of  macular  vision 
in  both  eyes. 

Auditory  Paths. — ^There    are   two   auditory  paths,   cochlear 
and  the  vestibular.     The  former  is  concerned  with  hearing  and 
the  latter  with  eqidlibrium. 
25 


386  TRACING    OF    IMPULSES. 

1.  The  Cochlear  Path  (Figs.  89,  70  and  54). — ^Impulses  of  hear- 
ing originate  in  the  organ  of  Corti.  They  are  transmitted  by 
the  rods  and  hair  cells  of  Corti  to  the  dendrites  of  the  spiral  gan- 
glion. Traversing  the  dendrites  and  cell-bodies  of  that  ganglion, 
they  enter  the  axones,  which  form  the  cochlear  nerve,  and  run 
backward  to  the  terminal  nucleus  of  that  nerve  in  the  medulla. 
Both  the  ventral  and  the  lateral  portions  of  the  cochlear  nucleus 
receive  the  impulses  of  hearing.  From  the  cochlear  nucleus  they 
run  either  lateral  and  dorsal  to  the  restiform  body  and  cross  to 
the  opposite  side  through  the  medullary  striae  and  trapezoid  body, 
or  they  run  medial  to  the  restiform  body  and  enter  at  once  into 
the  trapezoid  body.  By  either  course  they  reach  the  lateral  fil- 
let, and  chiefly  the  opposite  one.  The  lateral  fillets  conduct  the 
impulses  to  the  inferior  quadrigeminal  colliculi;  the  brachia  in- 
feriora  to  the  medial  geniculate  bodies,  and  the  temporo-thalamic 
radiations  to  the  third  and  fourth  fifths  of  the  superior  temporal 
and  to  the  transverse  temporal  gyri  of  the  cerebrum.  Through 
the  lateral  fillet,  impulses  producing  reflex  reach  the  quadrigemi- 
nal colliculi  and,  thence,  by  the  anterior  longitudinal  bundle, 
pass  to  motor  nuclei;  and,  also,  through  the  olivary  pedicle  and 
medial  longitudinal  bundle,  they  reach  the  nuclei  of  the  sixth, 
fourth  and  third  'cerebral  nerves. 

2.  Vestibular  Path. — ^The  extent  of  the  vestibular  conduction 
path  is  from  the  acustic  areas  of  the  utricle,  saccule  and  semi- 
circular canals  to  the  vestibular  nuclei  in  the  floor  of  the  fourth 
ventricle;  and,  thence,  to  the  cerebellum,  and  to  the  cortical  area 
of  equilibrium,  according  to  Mills,  in  the  temporal  cortex.  It  is 
the  path  of  space  sense.  Through  the  vestibular  nerve  the  im- 
pulses reach  the  dorso-medial,  the  dorso-lateral  and  superior  nu- 
cleus, and  the  nucleus  of  the  descending  root  in  the  floor  of  the 
fourth  ventricle. 

The  impulses  may  pursue,  from  the  terminal  nuclei  in  the  ven- 
tricular floor,  either  a  direct  or  an  indirect  course  to  the  cerebral 
cortex. 

(i)  ^^^  the  direct  course  they  run  through  the  opposite  medial 
fillet  and  certain  fibers  in  the  cortical  fillet,  perhaps  the  ventral 
stalk  of  the  thalamus,  to  the  middle  and  inferior  temporal  gyri. 


AFFERENT,  OR  SENSORY  PATHS. 


387 


LATERAL  GENIC- 
ULATE BODY 


Fig.  III. — The  optic  path.     (Original.) 


AFFERENT,  OR  SENSORY  PATHS.  389 

(2)  The  impulses  run  to  the  cerebellum,  by  the  indirect  course, 
through  the  descending  root,  and  the  external  arcuate  fibers  in 
the  restiform  body.  They  thus  reach  the  cerebellar  cortex.  They 
may  excite  in  the  cerebellum  impulses  of  equilibrium  and  then 
continue  upward.  From  the  cerebellum  the  course  of  the  impul- 
ses is,  presumably,  through  the  brachium  conjunctivum  to  the 
red  nucleus  and  thalamus  of  both  sides  and  thence  to  the  cortex. 

Impulses,  believed  to  be  concerned  with  reflexes,  run  from  the 
vestibular  nuclei  in  the  floor  of  the  fourth  ventricle,  (a)  to  the  oppo- 
site nuclei  of  motor  cerebral  nerves  via  the  medial  longitudinal 
bundle;  (b)  to  the  quadrigeminal  colliculi  through  the  superior 
fillet;  (c)  to  the  cerebellum  by  way  of  the  descending  root  and 
arcuate  fibers,  whence  they  reach  the  spinal  nerves  through  the 
descending  anterior  cerebello-spinal  tract;  (d)  to  the  spinal  cord 
and  nerves  through  the  axones  of  Deiters's  nucleus;  and,  perhaps, 
less  directly  through  the  vestibulo-oKvary  and  oHvo-spinal  fibers 
of  Kolliker. 

The  Gustatory  Paths. — ^They  extend  from  the  tongue  to  the 
nucleus  tractus  solitarii  in  the  medulla  and  thence,  probably, 
through  the  opposite  formatio  reticularis  and  internal  capsule 
to  the  taste  area  in  the  gyrus  fusiformis  (Mills)  or  gyrus  cinguli 
(Flechsig).  There  are  two  paths  from  the  tongue  to  the  nucleus 
of  the  solitary  tract.-  Those  impulses  from  the  base  of  the  tongue 
and  the  palate  run  through  the  ninth  nerve  and  those  from  the 
anterior  two-thirds  of  the  tongue  through  the  chorda  tympani 
and  intermediate  nerve  to  the  medulla  (A.  F.  Dixon,  Keen  and 
Spiller,  H.  Gushing,  etc.).  Possibly,  gustatory  impulses  origin- 
ating in  the  palate  may  traverse  the  descending  branches  of 
Meckel's  ganglion  and  the  great  superficial  petrosal  nerve  to  reach 
the  geniculate  ganglion  on  the  facial;  and,  then,  continue  through 
the  intermediate  nerve  to  the  solitary  tract.  All  impulses  arriving 
at  this  nucleus  of  the  solitary  tract  probably  complete  their  journey 
in  two  stages :  First,  through  the  formatio  reticularis  to  the  oppo- 
site thalamus;  and,  second,  through  internal  capsule  to  the  cortex. 

Destruction  of  the  olfactory  conduction  path  on  one  side 
causes  anosmia  on  the  same  side;  of  the  optic  tract  or  radiation, 
atrophy  and  destruction  in  the  corresponding  halves  of  both  retinae; 


39©  TRACING    OF    IMPULSES. 

of  the  auditory  path  above  the  pons,  deafness  chiefly  on  the 
opposite  side;  and  interruption  of  the  gustatory  path  above  the 
medulla  oblongata  abolishes  taste  on  the  opposite  (?)  side. 

III.     REFLEX  PATHS. 

There  is  no  visible  limit  to  the  number  of  reflex  paths.  Hence 
no  attempt  will  be  made  to  give  them  completely,  but  a  few  ex- 
amples of  various  kinds  will  be  given  which  may  assist  the  student 
to  trace  others  and  be  suggestive  of  their  great  multiplicity  and 
importance.  Under  certain  conditions,  unquestionably,  the  sen- 
sory and  motor  paths  that  have  been  traced  are  but  the  afferent 
and  efferent  limbs  of  reflex  arcs. 

Reflex  arcs  are  formed  (i)  by  the  sensory  and  motor  fibers 
of  spinal  nerves,  associated  in  the  gray  matter  of  the  cord;  (2) 
by  the  sensory  and  motor  fibers  of  cerebral  nerves,  which  are 
connected  in  the  brain;  (3)  by  afferent  spinal  fibers  connected 
by  the  ascending  fibers  of  the  medial  longitudinal  bundle,  with 
efferent  cerebral  fibers;  and  (4)  by  afferent  cerebral  and  efferent 
spinal  nerve  fibers,  the  two  being  associated  by  the  anterior 
longitudinal  bundle,  the  ponto-spinal  tracts,  the  fasciculi  proprii, 
the  spinal  tract  of  the  fifth  nerve,  the  vestibulo-spinal  tract,  the 
sohtary  tract,  etc. 

(i)  Spinal  Reflexes  (Figs.  112  and  113). — ^In  the  simplest 
spinal  reflexes,  the  afferent  fibers  of  the  arc  arborize  about  the 
cell-bodies  whose  axones  constitute  the  efferent  fibers;  the  affer- 
ent and  efferent  fibers  are  connected  by  one  set  of  intervening 
neurones  in  the  next  grade  of  reflex  arc.  Among  these  are  the 
skin  and  muscle  reflexes,  such  as  the  plantar,  the  patellar,  the 
gluteal  and  the  cremaster  reflexes,  the  involuntary  withdrawing 
of  a  part  from  a  source  of  irritation,  etc. 

Coordinating  and  equilibrating  reflex  impulses  traverse  much 
longer  arcs.  They  are  composed  of  the  spinal  ganglion  neurones, 
the  external  arcuate  fibers  (and  probably  the  [posterior]  cerebello- 
spinal tract)  in  the  afferent  limb,  and  the  descending  anterior 
cerebello- spinal  tract  and  the  anterior  root  neurones  in  the  effer- 
ent limb  of  the  reflex  arc. 


REFLEX    PATHS. 


391 


More  complicated  spinal  reflexes  arc  those  of  defecation,  mic- 
turition, parturition,  vasomotor  reflexes,  cardio-accelerator  reflexes, 
etc.  The  impulses  traverse  at  least  three  neurones  in  these  reflexes; 
because  all  efferent  white  rami  communicantes  terminate  in  some 
ganglion  proximal  to  the  organ  supplied.  As  an  example,  trace 
a  defecation  reflex. 

Defecation  Reflex. — ^The  rectum  is  supplied  by  the  third  and 
fourth  sacral  nerves  and  by  branches  of  the  inferior  mesenteric 
and  hypogastric  plexuses.  Irritation  of  the  sensory  endings  in 
the  mucous  membrane  is  caused,  normally,  by  the  presence  of 
feces.  The  impulses  caused  thereby  run  to  the  special  defecation 
center  in  the  lumbar  enlargement  of  the  spinal  cord,  either  by 


Fig.   112. — Diagram  of  a  simple  reflex  arc.     (Mier  Brubaker.) 

I.  Sentient   surface.     2.    Afferent   nerve.    3.    Emissive   or  motor  cell.    4.  Efferent   nerve- 

5.  Muscle. 


way  of  the  sacral  nerves  or  through  the  sympathetic  plexuses, 
the  ganglionated  cord,  and  the  rami  communicantes  to  the  lumbar 
nerves,  through  the  posterior  roots  of  which  they  reach  the  center 
in  the  cord.  From  the  defecation  center  the  impulses  pursue 
two  courses:  (a)  They  descend  through  the  third  and  fourth 
sacral  nerves  and  cause  inhibition  in  the  circular  fibers  of  the 
rectum  and  contraction  of  the  longitudinal  muscle,  (b)  This 
action  is  immediately  followed  by  impulses  which  pursue  the 
sympathetic  course,  through  the  anterior  roots  of  the  lumbar 
nerves,  the  rami  communicantes,  the  ganglionated  cord,  and  the 
inferior  mesenteric  and  hypogastric  plexuses,  to  the  rectum. 
They  cause,  in  succession  from  aboA'c  downward,  contraction 
of  the  circular  muscle  of  the  rectum.     The  two  series  of  impulses 


392 


TRACING    OF    IMPULSES. 


thus  open  a  way  for  the  passage  of  fecal  matter;  and,  then,  force 
it  through  the  opening  unless  prevented  by  the  voluntary  contrac- 
tion of  the  external  sphincter. 

(2)  Cerebral  Reflexes. — ^The  simplest  of  these  reflexes  are 
such  as  spasm  of  the  muscles  of  mastication  caused  by  a  bad 
tooth,  in  which  both  limbs  of  the  arc  are  formed  by  the  trigeminal 
nerve.  Again,  the  facial  expression  of  pain  due  to  the  same 
cause.     In  this  the  impulses  traverse  the  trigeminal  nerve  and 


Fig.  113. — A  more  complicated  spinal  reflex  arc,  involving  the  fasciculi  proprii. 
{Brubaker  after  KoUiker.) 

Diagram  showing  the  relation  of  the  third  neurone  a,  to  the  afferent  neurone  b,  and  to  the 
efferent  neurones  c,  c,  c. 


by  the  collaterals  of  its  root-fibers  reach  the  nucleus  of  the  facial. 
Through  the  facial  they  cause  contraction  of  certain  muscles  of 
expression.  Facial  spasm  in  tic  douloureux  is  due  to  the  same 
reflex.  The  involuntary  expansion  of  the  nostrils  upon  the  detec- 
tion of  a  faint  odor  is  due  to  an  olfactory-facial  reflex.  The  con- 
nection of  the  terminal  nucleus  and  cortical  center  of  the  olfactory 
nerve  with  the  genetic  nucleus  of  the  facial  nerve  is  very  much 


REFLEX   PATHS. 


393 


in  doubt;  it  may  be  established  in  part  (i)  by  the  fornix,  the 
thalamo-mammillary  bundle  and  thalamo-spinal  fibers,  (2)  by 
the  fornix,  medullary  stria,  fasciculus  retroflexus  and  descending 
fibers  of  the  interpeduncular  ganghon,  and,  (3)  by  the  fornix  and 
the  pedunculo-mamillary  bundles.  Squinting,  due  to  bright  light, 
is  produced  by  an  arc  composed  of  the  visual  path,  the  corticifugal 
part  of  the  occipito-thalamic  radiation,  the  anterior  longitudinal 
bundle  and  the  facial  nerve.  Substitute  the  oculomotor  nen'c 
for  the  facial  and  we  have  the  arc  for  pupillary  contraction  under 
the  same  conditions. 

Salivary  reflexes,  in  which  the  sight  of  a  fine  dinner  or  the  smell 
of  it  causes  the  flow  of  saliva ;  coughing,  sneezing,  vomiting  reflexes 
and  deglutition  reflexes  are  complicated,  but,  knowing  the  nerve 
supply  of  the  parts  involved,  the  student  should  try  to  trace  the 
impulses. 

(3)  Spino-cerebral  Reflexes. — ^Impulses  received  by  the  spinal 
cord  through  the  afferent  fibers  of  its  nerves  are  transmitted  by 
the  medial  longitudinal  bundle,  the  fasciculi  proprii  and  formatio 
reticularis  to  the  nuclei  of  motor  cerebral  nerves.  Thus  is  brought 
about  the  movement  of  the  head  and  eyes  toward  the  source  of 
impulse,  a  change  of  facial  expression  to  agree  with  the  painful 
or  pleasing  character  of  the  impulses,  etc. 

(4)  Cerebro-spinal  Reflexes. — Of  these  there  are  many.  Let 
us  notice  three. 

Respiratory  Reflex. — ^Any  obstruction  or  irritation  in  the  larynx 
or  trachea  sends  an  impulse  through  the  vagus  nerve  to  its  sensory 
nucleus  and,  through  its  descending  branches,  in  the  sohtary 
tract,  to  the  nucleus  ambiguus  and  nucleus  of  the  phrenic  nerve 
in  the  cervical  cord,  causing  increased  respiratory  efforts,  coughing, 
spasm  of  muscles  closing  glottis,  etc. 

Equilibrium  Reflex  (Vestibulo-spinal  Reflex). — ^The  simplest 
arc  of  equilibrium  between  the  eighth  cerebral  nerve  and  the 
spinal  nerves  is  formed  by  the  neurones  of  the  vestibular  ganglia 
(Scarpa's),  the  vestibulo-spinal  part  of  the  descending  anterior 
cerebello-spinal  tract  and  the  motor  neurones  of  the  anterior 
columna  of  the  spinal  cord.  A  more  complicated  arc  includes 
the  descending  root  of  the  vestibular  nerve,  the  external  arcuate 


394  TRACING    OF    IMPULSES. 

fibers  from  the  nucleus  funiculi  cuneati  and  the  descending  anterior 
cerebello-spinal  tract. 

Pupillary  Re-flexes. — Pupillary  dilatation  belongs  to  the  cerebro- 
spinal group  of  reflexes.  The  cilio-spinal  center  is  in  the  cervical 
enlargement  of  the  spinal  cord.  It  receives  optic  impulses  through 
the  anterior  longitudinal  bundle  from  the  corpora  quadrigemina. 
The  superior  quadrigeminal  colliculi  receive  those  impulses  by 
two  routes:  First,  directly,  through  the  fibers  of  the  lateral  root 
of  the  optic  tract,  and,  second,  indirectly,  through  corticifugal 
fibers  in  the  occipito-  thalamic  radiation,  and  the  brachium  supe- 
rius.  By  the  latter  route,  the  optic  impulses  which  have  reached 
the  visual  area  of  the  occipital  lobe,  by  way  of  the  intrinsic  retinal 
neurones  and  the  optic  nerves,  tracts  and  radiation,  are  returned 
to  the  lateral  geniculate  and  superior  quadrigeminal  bodies. 
Thence,  reaching  the  cilio-spinal  center  through  the  anterior 
longitudinal  bundle,  the  impulses  take  the  following  course: 
They  leave  the  spinal  cord  through  the  anterior  roots  of  the  upper 
thoracic  nerves  and  run,  in  succession,  through  the  rami  communi- 
cantes,  the  cervical  cord  of  the  sympathetic,  the  cavernous  plexus, 
the  ciliary  ganglion  and  the  short  ciHary  nerves  to  the  radiating 
fibers  of  the  iris,  causing  dilatation  of  the  pupil. 

For  pupillary  constriction,  the  impulses  run  directly  from  the 
superior  quadrigeminal  colliculus  to  the  oculomotor  nucleus, 
traversing  the  anterior  longitudinal  bundle  only  through  the 
dorsal  tegmental  decussation  (Meynerti).  Then,  through  the 
third  and  short  ciliary  nerves,  they  reach  the  sphincter  pupillae 
muscle. 


CHAPTER  VIII. 
EMBRYOLOGY  OF  THE  BRAIN  AND  SPINAL  CORD. 

The  brain  and  spinal  cord  are  developed  from  the  neural  tube; 
the  spinal  and  sympathetic  ganglia  and  the  ganglia  of  sensory 
cerebral  nerves  are  derivatives  of  the  neural  crest  (Figs.  i6  and 
114). 

Very  soon  after  conception  there  appears  along  the  median 
line,  in  the  back  of  the  embryo,  a  plate  of  epiblast,  called  the 
medullary  plate.  That  plate  soon  presents  two  longitudinal  eleva- 
tions, the  medullary  ridges,  separated  by  a  median  furrow,  the 
neural  groove  (Fig.  16).  At  first  the  medullary  plate  is  formed  of 
a  single  layer  of  columnar  cells;  but  those  cells  undergo  rapid 
mitosis,  as  the  medullary  ridges  are  developed,  and  arrange  them- 
selves in  several  layers  which  thus  bound  the  neural  groove  (Fig. 
114).  The  infolding  of  the  medullary  ridges,  together  with  their 
rapid  growth,  roofs  over  and  closes  in  the  neural  groove  and  pro- 
duces the  neural  tube  (Fig.  16).  The  tube  is  first  formed  in  the 
cer\'ical  region,  whence  the  fusion  of  the  medullary  ridges  extends 
in  both  directions.  By  the  approximation  of  the  medullar}^  ridges 
a  slight  paramedian  crest  is  produced  on  either  side,  called  the 
neural  crest.  The  neural  tube  and  the  neural  crest  are  nearly 
complete  by  the  fifteenth  day  after  conception,  the  groove  is  open 
only  at  the  position  of  the  future  median  aperture  of  IMagendie. 
Both  ends  of  the  tube  are  open  for  a  short  time,  the  anterior 
closing  first.  The  mesoblast  which  later  grows  around  the 
neural  tube  is  developed  into  the  meninges  and  the  surrounding 
bones,  which  inclose  the  cerebro-spinal  axis. 

The  Neural  Tube  (Figs.  16  and  114). — It  is  well  formed  at 
the  fifteenth  day.  The  cephalic  end  of  the  tube  is  much  larger 
than  the  caudal  end,  and  presents  at  this  time  two  constrictions 
that  separate  the  primary  brain  vesicles  from  one  another — 
the  anterior,  the  middle,  and  the  posterior.     Behind  the  posterior 

395 


396 


EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD. 


primary  vesicle,  the  neural  tube  remains  small  and  of  nearly 
uniform  size;  that  part  forms  the  spinal  cord,  in  which  the  general 
plan  of  development  may  be  observed  in  its  simplest  form. 


Fig.  114. — Sections  showing  stages  in  the  conversion  of  the  medullary  groove  into 
the  neural  canal.  From  the  tail  end  of  an  embryo  of  the  cat.  (Gordinier  after 
E.  A.  Schdfer.) 

ep,  me,  hy.  Epiblast,  mesoblast,  and  hypoblast,  m.g.  Medullary  groove,  n.c.  (in  IV). 
Neural  canal,    ch.  Notochord.     cce.  Celom.     am.  Tail-fold  of  the  amnion. 

In  the  very  early  stages  of  development  two  varieties  of  cells 
make  up  the  neural  tube  (Fig.  115).  Certain  very  long  cells, 
during  the  karyokinetic  growth,  arrange  themselves  at  right  angles 


EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD. 


397 


to  the  axis  of  the  tube.  They  are  the  ependymal  cells,  which 
form  a  supporting  framework  for  the  more  important  elements. 
They  reach  from  the  lumen  of  the  tube  to  its  peripheral  surface 
and  possess  nuclei  which  are  situated  largely  in  the  central  half 
of  the  cell.  The  peripheral  parts  of  the  ependymal  cells,  by 
irregular  branching  and  vacuolation,  form  a  protoplasmic  net- 
work destitute  of  nuclei,  called  the  marginal  velum.  This  marginal 
velum  forms  a  peripheral  zone  which  comprises  the  outer  one- 


Fig.   115. — Two  histologic  layers  in  the  embryonic  spinal  cord,  embryo  4.25  mm. 
long.     (McMurrich  after  His.) 

mv.  Marginal  velum  formed  by  peripheral  ends  of  ependymal  cells,  indifferent  cells  among 

their  bases. 


sixth  of  the  neural  tube.  The  inner  three-fourths  or  five-sixths 
of  the  tube  constitutes  a  thick  central  zone  in  which  are  the  bodies 
of  the  ependymal  cells  and,  among  their  bases,  a  variety  of  cells 
possessing  large  nuclei  and  small  protoplasmic  bodies  (Fig.  115). 
The  destination  of  the  latter  cells  cannot  yet  be  determined,  so 
they  are  named  the  indifferent  cells   (Fig.   116).     In  the  nuclei 


398 


EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD. 


of    the  indifferent  cells  all  forms  of  karyokinetic  figures  may  be 
seen.     This  fact  shows  that  they  are  rapidly  multiplying. 

In  a  somewhat  later  stage  of  development  the  indifferent  cells 
wander  outward  toward  the  marginal  velum  and  arrange  them- 
selves into  a  definite  layer,  known  as  the  mantle  layer  (Figs.  ii6 
and  127).  Three  concentric  zones  are  clearly  visible  at  this  time 
in  a  cross  section  of  the  neural  tube ;  the  marginal  velum,  the  man- 
tle layer,  and  the  ependymal  layer  formed  by  the  bases  of  the  epen- 
dymal  cells.  As  the  indifferent  cells  multiply  in  the  mantle  layer 
they  become  specialized  into  two  types,  the  neuroblasts  and  the 


Fig.  116. — Diagram  showing  development  of  neurones  in  the  spinal  cord. 

{McMiirrich  after  Schdfer.) 

The  circles,  indifferent  cells;  circles  with  dots,  neuroglia  cells;  shaded  cells,  germinal  cells; 
circles  with  cross,  germinal  cells  in  mitosis;  black  cells,  nerve-cells. 


Spongioblasts.  The  neuroblasts  are  the  larger.  They  are  the 
embryonic  neurones.  Each  neuroblast  throws  out  a  protoplasmic 
process  which  develops  into  an  axone  and  grows  outward  into  the 
marginal  velum.  Within  the  marginal  velum  the  axone  either 
runs  some  distance  and  returns  to  the  mantle  layer,  or  it  passes 
outward  through  the  marginal  velum  and  becomes  an  efferent  or 
motor  root-fiber.  Collaterals  are  given  off  from  the  axones,  the 
end-tufts  are  formed  and  the  medullary  sheath  is  laid  down  as 
development  proceeds  and  function  begins.     While  these  events 


EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD. 


399 


are  occurring  in  the  eflferent  part  of  the  neuroblast,  other  processes, 
called  dendrites,  are  given  off  by  the  cell-body.  They  belong  to 
the  afferent  side  of  the  cell.  There  are  usually  several  dendrites. 
They  branch  richly  close  to  the  cell-body  and  terminate,  as  a 
rule,  within  the  mantle  layer.  The  spongioblasts  are  the  smaller 
of  the  indifferent  cells.  They  are  primitive  neuroglia  cells  (Fig. 
53).  The  spongioblasts  develop  many  very  slender  and  richly 
branched  processes  of  ray-like  or  arborescent  form,  which  by  their 
interlacement  constitute  a  delicate  supporting  reticulum.  The 
neurones  are  held  in  the  meshes  of  this  reticulum,  and  both  the 
neurones  and  neurogha  cells  are  still  further  supported  by  a  coarse 
mesoblastic  framework  produced  by  the  ingrowth  of  blood  vessels. 
Zones  (Figs.  117  and  127). — ^While  the  neurones  and  neurogUa 
cells  are  forming,  there  occurs  in  each  lateral  wall  of  the  neural 


Fig.   117. — Transverse  section  of  the  cervical  part  of  the  spinal  cord  of  a  human 
embryo  of  six  weeks.     {Gordinier  siiter  Kolliker,  from  Quain.) 

c.  Central  canal,  e.  Its  epithelial  lining,  e.  (Superiorly)  The  original  place  of  closure  of 
the  canal,  a.  The  white  substance  of  the  anterior  columns,  g.  Gray  substance  of  anterior 
columna.     p.  Posterior  column,     ar.  Anterior  roots,     pr.  Posterior  roots. 


canal  a  longitudinal  evagination.  Tliis  evagination  produces  a 
longitudinal  groove  on  the  ventricular  surface  of  the  neural  tube, 
which  divides  it  into  a  ventral  and  a  dorsal  zone.  The  ventral 
zone  is  largely  efferent  in  function,  hence  from  it  issue  the  out- 
going tracts  (Figs.  127  and  128).  It  is  composed  of  a  median 
floor  plate  and,  on  either  side,  of  a  basal,  or  ventral  lamina.  The 
dorsal  zone  is  made  of  up  two  alar,  or  dorsal  laminae  joined  by 


400  EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD. 

the  median  roof-plate.  The  dorsal  zone  is  afferent  in  function 
and  in  connection  with  it  the  sensory  nerves  terminate.  The 
roof-plate  and  the  floor-plate  take  httle  or  no  part  in  forming  neu- 
rones; they  lack  the  mantle  layer,  and  are  composed  of  neurogha 
and  ependymal  cells. 

The  Neural  Crest  (Figs.  16  and  114). — (i)  The  cephalic  por- 
tion of  the  neural  crest  becomes  broken  into  five  pairs  of  gangha, 
which,  during  development,  shift  their  positions  to  the  ventral 
side  of  the  brain.  Those  ganglia  are  called  the  vagus,  glos; 
sopharyngeal,  geniculate,  auditory  and  semilunar  (Gasseri). 
Later,  the  auditory  gangha  lie  between  the  geniculate  and  glos- 
sopharyngeal ganglia.  These  five  ganglia  give  origin  to  the 
sensory  parts  of  the  vagus,  glossopharyngeal,  intermediate  and 
trigeminal  nerves;  and  to  all  of  the  acustic  nerve.  In  all  the  gan- 
glia except  the  auditory,  the  cells  develop  into  unipolar  neurones; 
they  remain  bipolar  in  the  auditory  ganglia.  The  unipolar  con- 
dition is  produced  by  the  growth  of  the  cell-body  toward  the.  sur- 
face of  the  ganglion  and  the  shifting  of  both  processes  to  the  same 
side  of  the  cell-body,  together  with  the  elongation  of  the  common 
point  of  attachment.  The  single  processes  of  the  unipolar  neu- 
rones immediately  divide,  T-like,  into  peripheral  and  central  fibers, 
which  in  appearance  are  axones.  The  peripheral  fibers  form  the 
sensory  part  of  the  respective  nerves  and  conduct  impulses  to- 
ward the  cell-body,  hence  they  may  be  considered  dendrites  (Cajal) ; 
the  central  fibers,  the  axones  proper,  form  that  part  of  the  nerve 
which  extends  from  the  ganghon  into  the  dorsal  zone  of  the  em- 
bryonic brain.  All  the  central  axones  of  the  several  ganglia 
divide,  T-hke,  upon  entering  the  brain,  and  collaterals  rise  from  the 
undivided  fibers  and  ffom  both  branches  of  them.  These  axones 
and  collaterals  arborize,  chiefly,  in  the  terminal  nuclei  of  the  res- 
pective nerves;  but  certain  of  them,  the  excito-reflex  fibers,  ter- 
minate in  nuclei  of  motor  nerves. 

The  development  of  peripheral  common  sensory  neurones,  both  cerebral 
and  spinal,  has  been  observed  in  certain  lower  vertebrates.  In  the  amblystoma 
punctatum  the  following  phases  have  been  observed:  i.  The  elongation  of  the 
cells  in  the  neural  crest  to  a  spindle-form.  2.  The  projection  of  a  slender 
central  process,   the  axone,  which  grows  into  the  neural  tube.     3.  A  thick 


THE    BRAIN.  4OI 

irregular  process,  the  dendrite,  is  thrown  out  from  the  peripheral  end  of  the 
cell;  later  it  becomes  smooth  and  fibrillar  in  character.  This  bipolar  cottdi- 
lion  persists  in  very  low  forms,  such  as  the  amphyoxus  and  cyclostomes. 
4.  In  bony  fishes  some  of  the  neurones  become  unipolar.  The  greater  num- 
ber become  unipolar  in  higher  vertebrates  (/.  B.  Johnston's  Nervous  System 
oj  Vertebrates). 

(2)  The  spinal  portion  oj  the  neural  crest  forms  the  thirty-one 
pairs  oj  spinal  ganglia  situated  on  the  posterior  nerve  roots; 
and,  also,  the  vertebral,  prevertebral  and  terminal  ganglia  of  the 
sympathetic  system.  The  sympathetic  ganglia  wander  uidely. 
In  them  the  epiblastic  cells  develop  into  multipolar  neurones, 
the  nonmedullated  processes  of  which  constitute  the  larger  num- 
ber of  gray  fibers  in  the  sympathetic  system.  The  cells  of  the 
spinal  ganglia  form  unipolar  neurones,  like  those  of  the  vagus, 
glossopharyngeal,  geniculate  and  semilunar  ganglia.  Like  them, 
also,  the  single  processes  divide,  T-like,  the  peripheral  arms 
of  the  T-branches  forming  the  sensory  part  of  each  spinal  nerve 
and  the  central  arms  (the  axones)  the  posterior  roots  of  those 
nerves.  The  latter  enter  the  cord  at  the  posterior  lateral  sulcus 
and,  before  and  after  dividing  T-Hke  into  an  ascending  and  a 
descending  branch,  give  off  collaterals.  The  descending  fibers, 
long  and  short,  arborize  and  end  in  the  gray  matter  of  the  posterior 
columna,  the  center  of  the  crescent  and  the  anterior  columna,  the 
long  fibers  forming  the  postero-medial  and  postero-lateral  descend- 
ing radicular  tracts;  the  ascending  axones  and  collaterals  termin- 
•ate  in  the  gray  substance  of  the  spinal  cord  and  in  the  nuclei 
of  its  posterior  columns,  namely,  the  nucleus  funicuH  gracihs 
and  nucleus  funiculi  cuneati  of  the  medulla.  The  long  ascend- 
ing fibers  form  the  postero-medial  tract  (Goll's)  and,  the  postero- 
lateral tract  (Burdach's);  and,  the  shorter  ones,  those  reaching 
but  a  few  segments,  make  up  the  marginal  tract  of  Lissauer. 
The  greater  number  of  posterior  root-fibers  terminate  in  the  gray 
substance  at  or  near  their  level  of  entrance  into  the  cord. 

THE  BRAIN. 

The  primary  brain  vesicles  grow  rapidly.     By  the  end  of  the 
fourth  week  a  constriction  is  visible  in  the  anterior  primary  vesicle 


402  EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD. 

and  another  in  the  posterior  primary  vesicle,  dividing  each  into 
two  and  making  in  all  -five  secondary  train  vesicles^  which  freely 
communicate  with  one  another  and  are  numbered  from  before 
backward.     They  are: 

1.  Telencephalon. 

2.  Diencephalon. 

3.  Mesencephalon. 

4.  Metencephalon. 

5.  Myelencephalon. 

These  vesicles  form  the  brain,  their  cavities  becoming  the  ven- 
tricles (Figs.  118,  120  and  17).  The  neuroblasts  of  the  mantle 
layer  produce  the  neurones,  whose  cell-bodies  and  dendrites  are 
found  in  the  cortex  and  ganglia,  and  whose  meduUated  axones 
form  the  white  substance. 

Flexures  (Fig.  118). • — ^The  cephalic  portion  of  the  neural  tube 
is  the  seat  of  three  flexures,  two  ventral  and  one  dorsal,  (i)  The 
mesencephalic  flexure  (ventral)  begins  very  early  and  amounts  to 
nearly  180  degrees  by  the  twenty-eighth  day.  It  bends  ventrally 
the  diencephalon  until  it  almost  touches  the  metencephalon.  Thus 
the  inter-brain  and  pons  are  approximated  and  the  mid-brain 
almost  concealed.  (2)  The  cervical  flexure  is  also  a  ventral  one. 
It  is  located  at  the  junction  of  the  fifth  vesicle  with  the  spinal 
cord,  and  corresponds  to  the  bending  of  the  head  upon  the  body 
of  the  embryo.  This  flexion  begins  about  the  twenty-first  day. 
By  the  end  of  the  fourth  week,  it  is  completed  and  amounts  to 
90  degrees.  (3)  The  dorsal  flexure  is  beginning  to  form  at  the 
same  time  (fourth  week).  It  occurs  between  the  fourth  and  fifth 
brain  vesicles,  and  is  often  called  the  metencephalic  flexure.  It 
reaches  180  degrees  by  the  eighth  week,  when  the  dorsal  part 
of  the  metencephalon  (the  cerebellum)  rests  upon  the  medulla 
oblongata.  The  convexity  is  formed  by  the  pons,  hence  the 
synonym,  pontine  flexure.  The  cervical  and  metencephalic  flex- 
ures almost  entirely  disappear,  but  the  mesencephalic  flexure  is 
permanent. 


THE    BRAIN. 

TABLE  IV. 


403 


BRAIN  VESICLES,  THEIR  DERIVATIVES  AND  VENTRICLES 

(Figs.  17,  118  and  120). 


Primary  Vesicles. 


Anterior — the  Pros- 
encephalon      o  r  -^ 
Fore-brain. 


Secondary  Vesicles. 

Telencephalon, 
Lateral  ventricle  and 
Aula  of    third    ven- 
tricle. 

Diencephalon,  and 
Third  ventricle,  except 
the  aula. 


Derivatives. 


[>  Cerebrum. 


Middle— the  Mes- 
encephalon, or 
Mid-brain. 

Posterior —  the 
Rhombencepha- 
lon. 


]  Mesencephalon,  and 
1       aqueductus  cerebri. 

r  Isthmus    rhomben-  ^ 

J       cephali  I  Rhombencephalon  and 

1   Metencephalon  j  Fourth  ventricle. 

I  Myelencephalon.  J 


TABLE  V. 


SECONDARY  BRAIN  VESICLES  AND  THEIR  DERIVATIVES. 


Telencephalon 
(End-brain) 


f  Neopalliur 
A  Rhinencep 
(_  Corpus  striatum. 

(Chiasma  opticum 
Lamina  terminalis 
Tuber  cinereum    ■ 


Thalamencephalon. 


Diencephalon       ) 
(Inter- brain) 


^  Hypophysis. 
Thalamus 

Metathalamus 

1 

1^  Epithalamus 


(  Corpora 
(  Geniculata 
\  Epiphysis,  and 
(  Xuc.  habenulai 


I    Pars  mammillaris  hv-  ( 

I  .11-  '     ^  Corpora  mammiUaria. 

^      pothalami.  (^         ^ 


404  EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD. 


Pedunculi  cerebri. 


Mesencephalon 
(Mid-brain) 


Lamina  quadrigemina. 


C  Bases  pedunculi 
-N  Substantia  nigra 
C  Tegmenta. 

f  Corpora  quadrigemina- 
Colliculi  superiores 
CoUiculi  inferiores 
Brachia — 

Brachia  superiora 
Brachia  inferiora. 


Metencephalon   - 


Isthmus     rhomben- 
cephali     (in    which 

are) 


Cerebellum. 


Pedunculi  cerebri 
Brachia  conjunctiva 
Velum  meduUare  superius. 

{  Cortex 
Corpus  meduUare 

Ganglia 

(Pedunculi  cerebelli) 
Vela  medullaria. 


In  the  following  resume  of  the  formation  of  the  central  nervous 
system,  I  have  drawn  so  largely  from  Prof.  McMurrich's  "Devel- 
opment of  the  Human  Body"  that  I  wish  at  this  point,  to  make 
grateful  acknowledgment  of  my  indebtedness  to  him. 


Pons  Varolii. 
Myelencephalon  \  Medulla  oblongata. 


Roof-plate 


TELENCEPHALON. 
TABLE  VI. 

DERIVATIVES  OF  TELENCEPHALON. 

(Modified  from  McMurrich  's  Embryology.) 

In  Median  Structures.  In  Hemisphere. 

Roof  epithelium  of  the  aula     i  Floor  of  chorioidal  fissure 
Lamina  terminalis  (in  part). 


f  Neopallium 

DorsalLamina  i  ^""?'^^  '^""^^"^'^  ^^"  P^^^        Rhinencephalon 
(  Optic  vesicle.  [  ^^^p^^  ^^^j^^^^^ 


THE    BRAIN. 


405 


Ventral  Zone     J       --^^^f?-" 
1  uber  cinereum 


Anterior  part  of  hypothal- 
amic region 
Tuber  cinereui 
Infundibulum. 


^  ,.  (  Falx  cerebri  ( 

Surroundins;      1-r.,     r,      ••,     i      ^,.,1,,     . 

M      Ki       't  chonoid  tela  of  third  ■<  Meninges. 

'       ventricle.  ' 

The  telencephalon  is  at  first  a  single  vesicle  forming  the  fore 
part  of  the  anterior  primary  vesicle,  and  for  a  time  is  open  in  front 
at  the  neuropore  (Fig.  118,  VI).  The  median  portion  of  its  an- 
terior wall,  lamina  terminalis,  remains  almost  stationary;  laterally, 
it  is  the  seat  of  rapid  growth. 

Optic  Vesicle. — ^Almost  before  the  telencephalon  is  differen- 
tiated from  diencephalon,  a  club-shaped  diverticulum,  called  the 
optic  vesicle,  is  thrown  out  from  the  ventral  part  of  its  dorsal 
zone.  It  grows  outward  and  forward,  separates  from  the  telen- 
cephalon and,  becoming  indented,  forms  the  oplic  cup,  from  which 
the  retina  is  developed.  The  point  of  origin  of  the  optic  vesicle 
is  indicated  in  the  adult  by  a  slight  pit,  termed  the  optic  recess. 
The  optic  recess  is  situated  between  the  lamina  terminalis  and  the 
columna  fornicis  at  the  anterior  end  of  the  sulcus  hypothalamicus 
(Monroi).  This  sulcus,  in  the  anterior  primary  vesicle,  sepa- 
rates the  ventral  from  the  dorsal  zone. 

Hemisphere  of  Cerebrum  (Figs.  17,  118  and  120). — Soon 
after  the  appearance  of  the  optic  vesicle,  a  large  bulging  occurs  on 
either  side  in  the  dorsal  zone  of  the  telencephalon.  That  bulging 
produces  a  hollow  diverticulum,  whose  cavity  is  the  primitive 
lateral  ventricle  and  whose  walls  form  the  substance  of  the  hemis- 
phere. The  outgrowth  is  called  the  hemisphere  vesicle.  Its 
constricted  stalk  contains  the  primitive  interventricular  foramen 
{Monroi,  Fig.  17).  The  vesicles  grow  forward  and  outward  at 
first,  separated  from  one  another  by  mesoblast  which  forms  the 
falx.  Later,  growth  occurs  in  succession,  upward,  backward  and 
downward,  until  by  the  seventh  month  the  hemisphere  overhangs 
every  other  part  of  the  brain.  The  hemisphere  vesicle  is  formed 
almost  wholly  by  the  dorsal  lamina  of  the  telencephalon  wliich 
grows  and  develops  wonderfully  and  will  be  considered  further 


4o6 


EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD. 


on.  It  also  contains  a  narrow  prolongation  of  the  roof-plate. 
This  prolongation  of  the  roof-plate  undergoes  very  little  develop- 
ment. At  first  it  is  placed  in  the  roof  of  the  hemisphere  vesicle; 
but  the  upward  growth  of  the  hemisphere  shifts  it  to  the  medial 
surface  and,  later,  the  backward  and  downward  extension  of  the 
hemisphere  carries  the  roof-plate  through  a  horse-shoe  curve 
down  toward  the  pole  of  the  temporal  lobe.  No  thickening  occurs 
in  this  prolongation.  Becoming  indented  longitudinally  it  forms 
the  floor  of  the  chorioidal  fissure  in  which  is  developed,  from 


0. 


112 


U' 


Fig.  1 1 8. — Median  section  of  embryonic  brain  of  the  third  month. 
(McMurrich  after  His.) 

I.  Myelencephalon.  II.  Metencephalon:  i,  Pons,  2,  Cerebellum.  III.  Isthmus  rhomb- 
encephali.  IV.  Mesencephalon:  i,  Pedunculi,  2,  Corpora  quadrigemina.  V.  Diencephalon: 
I,  Pars  mammillaris  hypothalami,  2,  Thalamus,  3,  Epithalamus.  VI.  Telencephalon:  i,  Pars 
optica  hypothalami,  2,  Corpus  striatum,  3,  Rhinencephalon,  4,  Neopallium. 


ingrowing  mesoblast,  the  chor'wid  plexus  of  the  lateral  ventricle 
(Fig.  119). 

Rhinencephalon  (Figs.  17,  118  and  120). — In  the  fifth  week 
a  hollow  diverticulum  grows  out  from  the  antero-inferior  wall  of 
the  hemisphere  vesicle  and  forms  a  prominent  lobe.  It  preserves 
a  lobular  form  in  the  horse,  and  in  some  other  animals;  but  in 
man  it  soon  becomes  constricted  by  the  sulcus  parolfactorius 
posterior  into  an  anterior  and  a  posterior  part,  and  loses  its  ven- 
tricular cavity.     The  anterior  part  develops  the  olfactory  bulb, 


THE    BRAIN. 


407 


■Ma,. 


Fig.   119. — Transverse  sections  through  the  fore-brain  of  a  four  and  one-half  weeks 
embr}'o.     (Gardinier  and  Quain  after  His.) 

A.  Through  the  lower  anterior  part  of  the  fore-brain.  S.  Falx.  Sf.  Fold  of  roof  passing 
below  falx  toward  the  third  ventricle.  Bf.  Fold  forming  the  fissura  hippocampi,  v.  RL,  h.  Rl. 
Anterior  and  posterior  parts  of  olfactory  lobe.  Cs.  Corpus  striatum.  O.W.  Groove  con- 
tinuous with  optic  stalk.     P.s.  Hypothalamus.     T.c.  Tuber  cinereum. 

B.  Section  a  little  farther  back.  Sf  is  replaced  by  a  less  prominent  but  broader  fold  of 
the  roof,  Ad,  .vhich  subsequently  receives  the  chorioid  vessels,  and  is,  therefore,  the  chorioid 
fold.  Hs.  Hemisphere  vesicle.  Th.  Thalamus.  S.M.  Sulcus  hypothalamicus  (Monroi), 
below  and  behind  the  thalamus. 

C.  Still  farther  back.  .-id.  Chorioid  fold  here  projecting  into  lateral  ventricles,  but  still 
free  from  mesoblast  and  blood-vessels.  Ma.  Mammillary  tubercle.  The  other  lettering  as 
before. 


THE    BRAIN. 


409 


tract,  triangle,  and  the  parolfactory  area  (Brocae),  the  posterior 
portion  forms  the  anterior  perforated  substance,  etc. 

Primary  Fissures  (Figs.  121  and  122). — ^The  vesicle  walls  are 
of  uniform  thinness  up  to  the  second  month.  During  their  rapid 
growth  in  the  second  and  third  months  they  become  thrown  into 
folds  wliich  encroach  upon  the  cavity  and  present  on  the  surface 
of  the  vesicle  (or  hemisphere)  the  primaiy  fissures.  The  cause 
of  the  infoldings  is,  perhaps,  the  resistance  of  the  slower  growing 
cranium.  The  primary  fissures  are  best  developed  in  the  third 
month.  They  consist  of  the  chorioidal  fissure,  already  mentioned, 
the  hippocampal  fissure  which,  surrounding  it,  is  concentric  with 


k  1.  m  n  o 

Fig.  120. — Diagrammatic  sagittal  section  of  vertebrate  brain. 

(Morris's  Anatomy  after  Huxley.) 

a.  Corpora  quadrigemina.  b.  Mid-brain,  c.  Pineal  body.  d.  Cerebellum  (hind-brain). 
e.  Medulla  oblongata  (after-brain),  f.  Pons  Varolii  (hind-brain),  g.  Lateral  ventricle. 
h.  Cerebral  hemisphere,  i.  Corpus  striatum,  j.  Olfactory  diverticulum,  k.  Pedunculi 
cerebri.  1.  Thalamus,  m.  Inter-brain,  n.  Hypophysis,  o.  Interventicular  foramen.  4. 
Fourth  ventricle,     s.  Aqueduct  of  cerebrum.     3.  Third  ventricle. 

it,  and  the  fossa  lateraHs  cerebri  (Sylvii).  The  hippocampal 
fissure  (Fig.  121)  begins  near  the  frontal  pole  on  the  medial  sur- 
face of  the  hemisphere  vesicle  and  extends  backward,  downw-ard 
and,  lastly,  forward  toward  the  temporal  pole.  It  divides  the 
medial  surface  into  a  broad  marginal  gyrus  and  the  dentate  g}'rus, 
the  latter  is  between  it  and  the  chorioidal  fissure.  In  its  whole 
course  it  is  parallel  with  the  chorioidal  fissure  (Figs.  119  and  121). 
The  ventricular  eminence  caused  by  the  hippocampal  fissure  is 
called  the  hippocampus.  The  hippocampal  fissure  gives  off  two 
branches  at  its  most  posterior  part,  which  represent  the  occipito- 
parietal and  the  calcarine  fissmrs  (Fig.  121).  Both  branches  pro- 
duce ventricular  eminences,  but  only  that  of  the  calcarine  per- 


4IO  EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD. 

sists,  in  the  calcar  avis.  The  primary  occipito-parietal  fissure 
entirely  disappears.  The  whole  superior  part  of  the  hippocam- 
pal  fissure  is  represented  in  the  adult,  as  to  position,  by  the  cal- 
losal  fissure.  The  lateral  cerebral  fossa  (Fig.  122)  is  a  deep  bay 
in  the  ventral  border  of  the  hemisphere  vesicle.  It  is  due  to  the 
relatively  limited  growth  of  the  corpus  striatum  in  comparison 
with  the  more  rapid  and  greater  growth  of  the  surrounding  parts. 
The  thickened  floor  of  the  fossa  cerebri  lateralis  develops,  inter- 
nally, the  corpus  striatum  and,  externally,  forms  the  insula  (Reili). 
The  lateral  fossa  and  the  four  fissures  mentioned  above  are  well 
formed  by  the  third  month,  but  the  lateral  cerebral  fossa  is  not 
converted  into  a  fissure  until  the  end  of  the  fifth  month.  Even 
then  only  the  posterior  ramus  of  the  fissura  cerebri  lateralis  (Sylvii) 
is  formed,  and  this  is  brought  about  by  the  meeting  of  the  temporal 
and  the  fronto-parietal  parts  of  the  operculum.  It  is  during  the 
first  year  after  birth  that  the  development  of  the  orbital  and 
frontal  parts  of  the  operculum  produces  the  anterior  horizontal 
ramus  and  the  anterior  vertical  ramus  of  this  fissure. 

Secondary  Sulci  and  Secondary  Fissure  (Fig.  123). — ^The 
secondary  sulci  are  linear  indentations  of  the  surface  only;  they 
cause  no  ventricular  eminences.  About  the  middle  of  the  fifth 
month  the  first  secondary  sulcus  makes  its  appearance.  It  is 
the  sulcus  cinguli  of  the  medial  surface,  which  separates  the  su- 
perior frontal  gyrus  and  paracentral  lobule  from  the  gyrus  cinguli 
of  the  adult  brain  (Fig.  27).  Its  development  in  two  or  three 
pieces  explains  its  irregularity  and  occasional  want  of  continuity. 
In  the  sixth  month  the  subparietal  and  occipito-parietal  sulci  are 
present.  There  is  no  sign  of  the  latter  sulcus  in  the  early  part 
of  the  fifth  month  and  the  permanent  sulcus  does  not  produce  a 
ventricular  eminence,  hence  the  occipito-parietal  indentation  is  a 
sulcus  and  not  a  fissure  (see  Cunningham  Memoirs).  Early  in 
the  sixth  month  the  most  important  of  the  remaining  sulci  are 
formed,  such  as,  the  central  sulcus  (Rolandi),  the  precentral,  the 
postcentral,  the  superior  temporal  sulcus  and  the  remaining  larger 
sulci  of  the  frontal,  parietal,  occipital  and  temporal  lobes  (Figs. 
23  and  123).  The  only  secondary  fissure,  the  collateral  fissure 
appears  in  the  same  month.     It  is  developed  on  the  tentorial  sur- 


THE    BRAIN. 


411 


face  of  the  hemisphere,  at  first,  in  three  separate  parts,  an  an- 
terior and  a  posterior  temporal  and  an  occipital  part.  Its  middle 
part  is  a  total  fissure,  so  is  its  anterior  part  sometimes.  When 
both  arc  total  they  produce  a  long  eminence  in  the  inferior  horn 
of  the  lateral  ventricle,  external  to  the  hippocampus  and  parallel 
with  it,  hence  its  name,  the  eminentia  collatcralis. 

There  are  many  tertiary  sulci  which  do  not  appear  until  near 
birth,  some  of  them  one  or  two  years  after  birth. 

Transverse  Fissure  of  the  Cerebrum. — Only  the  anterior  part 


Fig.  121. — Medial  sagittal  section  through  the  brain  of  an  embryo  of  three  months, 
showing  the  primitive  fissures  on  the  medial  surface  of  the  cerebral  hemisphere. 
{McMurrich  after  Mihalkovicz.) 

c.  Calcarine  fissure,  ca.  Anterior  commissure,  cc.  Corpus  callosum.  cf.  Chorioidal  fis- 
sure, dg.  Dentate  gyrus,  fm.  Foramen  interventriculare  (Monroi).  h.  Hippocampal  fissure. 
po.  Occipito-parietal  fissure. 

of  this  fissure,  which  is  between  the  fornix  and  the  inter-brain, 
belongs  wholly  to  the  cerebrum;  the  posterior  part  separates 
cerebrum  from  cerebellum.  The  anterior  part  of  the  transverse 
fissure  is  produced  by  the  backward  growth  of  the  united  cere- 
bral hemispheres  over  the  free  dorsal  surface  of  the  diencephalon, 
the  inter-brain.  It  is  continuous  laterally  with  the  chorioidal 
fissure  in  each  hemisphere  and  contains  the  chorioid  tela  of  the 
third  ventricle. 
Cerebral  Cortex  and  Medulla. — As  the  crvri  of  the  cerebrum 


412  EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD. 

are  acquiring  their  adult  forms  and  producing  the  various  fissures 
and  sulci,  the  walls  of  the  hemisphere  vesicle  thicken  rapidly  and 
give  rise  to  the  corpus  striatum,  the  cortex  and  the  medullary- 
substance;  but  the  order  of  development  is  not  yet  understood. 
The  development  of  the  gray  and  the  white  substance  contracts 
the  cavity  of  the  hemisphere  vesicle  to  the  size  of  the  lateral  ventricle;. 
and  the  cornua  of  the  ventricle  are  produced  by  the  forward,  back- 
ward, and  downward  growth  of  the  vesicle  in  the  successive  form- 
ative stages.  Little  is  known  of  the  time  at  which  the  cortical 
neurones  are  formed;  but  it  would  seem  that  they  continue  to 
undergo  medullation  and  to  become  functional  up  to  a  late  period 
of  life,  and  the  investigations  of  Kaes  support  this  inference. 

Fornix. — ^A  ridge  appears,  about  the  fourth  month,  on  the  medial 
surface  of  the  hemisphere  vesicle,  along  the  convexity  of  thechorioidal 
fissure.  That  ridge  reaches  from  the  lower  end  of  the  hippocampus 
to  the  roof  of  the  interventricular  foramen.  It  becomes  converted 
into  a  bundle  of  fibers  which  is  continued  into  the  lamina  terminalis 
and  then  through  the  lateral  wall  and  floor  of  the  diencephalon 
to  the  corpus  mammillare.  It  forms  a  lateral  half  of  the  fornix. 
The  union  of  the  two  halves  in  the  lamina  terminalis  forms  the 
primitive  body,  or  corpus  jornicis.  The  body  is  extended  by  the 
upward  and  backward  growth  of  the  lamina  terminalis  and  by 
the  crossing  over  of  certain  fibers  from  one  crus  fornicis  to  the 
Other,  which  results  in  the  formation  of  the  commissura  hippo- 
campi. 

Another  ridge,  a  slight  one,  appears  about  the  same  time  on 
the  opposite  lip  of  the  chorioidal  fissure.  It  represents  the  stria 
terminalis.  This  latter  ridge  and  the  fornix  ridge  bound  the  roof- 
plate  as  represented  in  the  hemisphere.  This  roof-plate  extension 
undergoes  no  development.  It  forms  the  chorioid  epithelial 
lamina  of  the  lateral  ventricle,  which  loosely  joins  the  fornix  and 
the  stria  terminalis,  being  folded  over  the  chorioid  plexus  of  that 
ventricle  (Fig.  119). 

Internal  Capsule. — ^It  is  formed  largely  along  the  Hne  of  fusion 
between  the  medial  surface  of  the  hemisphere  vesicle  and  the 
lateral  surface  of  the  diencephalon.  Motor  fibers  grow  down- 
ward through  the  corpus  striatum  from  the  cerebral  cortex,  and 


THE    BRAIN. 


413 


sensory  fibers  ascend  through  the  striated  body  to  the  cortex  from 
the  thalamus  and  other  gangha.  All  these  motor  and  sensory 
fibers  together  constitute  the  internal  capsule.  Its  bell-shape  in 
the  hemisphere  is  due  to  the  rotary  growth  of  the  hemisphere, 
upward,  backward,  downward  and  forward,  around  the  corpus 
striatum  (Figs.  32  and  ^,7,). 

Anterior  Commissure  (Fig.  121). — ^The  lamina  terminalis 
at  the  fourth  week  is  a  thin  median  plate  bounding  the  aula  an- 
teriorly and  joining  the  hemisphere  vesicles  together  just  in  front 
of  the  foramina  interventricularia  (Monroi)  (Fig.  17).  Its  ven- 
tral portion  remains  thin;  but  its  dorsal  part  thickens  greatly  and, 


Fig.  122. — The  fossa  lateralis  cerebri,  in  embryonic  brain  of  the  fourth  month. 
(After  McMurrich.) 

c.  Cerebellum,     p.  Pons.     s.  Fossa  lateralis  cerebri. 

with  the  upward  and  backward  growth  of  the  hemisphere,  it  is 
extended  in  a  crescent,  dorsal  to  the  interventricular  foramen, 
as  far  backward  as  the  splenium  of  the  corpus  callosum.  Within 
this  thickened  crescentic  part  of  the  lamina  terminalis  are  formed 
the  anterior  commissure,  the  body  0}  the  fornix,  the  corpus  callo- 
sum and  the  septum  pellucidmn.  The  anterior  commissure  is 
first  formed.  Through  the  ventral  angle  of  the  thickened  por- 
tion grow,  transversely,  the  commissural  and  the  decussating 
fibers  of  the  rhinencephalon  and  the  commissural  fibers  connect- 
ing the  occipito-temporal  cortices.  These  fibers  make  up  the 
anterior  commissure.     The  fornix  fibers  grow  for  the  most  part 


414 


EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD. 


longitudinally  through  the  zone  next  the  ventral  surface  of  the 
crescentic  lamina  and,  on  reaching  the  anterior  commissure,  bend 
backward  into  the  lateral  wall  of  the  aula  and  third  ventricle; 
a  certain  number  of  fornix  fibers  cross  over  in  the  posterior  border 
of  the  lamina  terminalis  and  produce  the  commissura  hippocampi. 
The  corpus  callosum  js  formed  in  the  dorsal  zone  of  the  crescentic 
lamina  terminalis. 

The  corpus  callosum    (Fig.  121)  is  produced  by  fibers  that 
grow  from  one  cerebral  hemisphere  to  the  other  through  the  fronto- 


J>tC 


Fig.   123. — Permanent   fissures  and  sulci  on  the  convex  surface  of  the  cerebrum 
as  seen  in  a  seven  months  embryo.     (McMurrich  after  Cunningham.) 

fs.  Superior  frontal  fissure,  ip.  Interparietal.  IR.  Island  (Reili).  pci.  Inferior  pre-central. 
pes.  Superior  pre-central.  ptc.  Post-central.  R.  Central  (Rolandi).  5.  Lateral  (Sylvii). 
fi.  First  temporal. 


dorsal  zone  of  the  lamina  terminalis.  The  different  parts  of  the 
corpus  callosum  are  formed  in  regular  order — rostrum,  genu, 
truncus,  splenium — and  this  order  coincides  with  the  lines  of 
growth  in  successive  stages  of  cerebral  development.  The  fibers 
of  the  corpus  callosum  pierce  the  dentate  gyrus  of  the  hemisphere 
vesicle.  In  so  doing,  they  completely  obliterate  the  superior  part 
of  the  hippocampus  and  leave  but  rudiments  of  the  dentate  gyrus, 
namely,  the  gyrus  supracallosus  and  gyrus  subcallosus  (longitu- 
dinal  stricB  and  peduncle  of  the  corpus  callosum),  the  fasciola 


DIENCEPHALON, 


415 


cinerca  and  the  small  dentate  fascia  of  the  adult  are  the  rudimen- 
tary remains. 

Septum  Pellucidum. — That  part  of  the  lamina  lerminalis 
which  is  included  between  the  corpus  callosum  and  the  body  of 
the  fornix  persists  as  the  septum  pellucidum.  It  develops  a  lymj)h 
space  in  the  median  plane,  called  the  fijlh  ventricle  (caviim  septi 
pellucidi)  and  becomes  so  thin  as  to  be  translucent. 

The  above  description,  giving  the  origin  of  the  septum  pellucidum,  corpus 
callosum  and  anterior  commissure  from  lamina  terminalis,  is  the  one  com- 
monly accepted;  but  it  is  not  their  origin  in  the  rabbit  (Marshall)  or  in  the 
rat  (Zuckerkandl),  and  there  is  still  room  for  doubt  concerning  their  origin  in 
the  human  brain.  It  is  possible  that  all  or  a  part  of  them  are  developed  in  a 
crescentic  area  of  fusion  between  the  cerebral  hemispheres,  as  in  lower  animals. 

The  pars  optica  hypothalami  (Fig.  118)  is  developed  in  the 
ventral  zones  of  the  telencephalon.  The  tuber  cinereum  and  the 
infundibulum  are  true  derivatives  of  these  telencephalic  zones, 
but  the  optic  chiasma  is  not.  It  is  produced  by  the  ingrowth  of 
fibers  from  the  retinas  and  the  medial  geniculate  bodies. 

DIENCEPHALON. 

This  is  the  posterior  division  of  the  anterior  primary  ATsicle. 
It  forms  the  inter-brain  and  contains  the  greater  part  of  the 
third  ventricle  (Figs.  17,  118,  V,  and  119).  Its  lateral  walls  pre- 
sent on  each  side  a  distinct  ventricular  sulcus,  the  sulcus  hypo- 
thalamicus  (Monroi)  (Fig.  119,  B  and  C)  which  separates  the  ven- 
tral zone  from  the  dorsal  zone  (?). 

TABLE  VII. 
DERIVATIVES   OF  THE  DIENCEPHALON. 

Derivatives. 

.    .  \  Roof  epithelium  of  third  ventricle. 

]  Corpus  pineale  (epiphysis). 

\  Thalamus 

I  Corpora  geniculata. 

I  Pars  mammillaris  hypothalami 

Ventral  Zone  -'       Corpus  mammillare 

(  A  small  part  of  tuber  cinereum. 

\  Chorioid  tela  and  plexus  of  lliini  ven- 
Surrounding  Mesoblast    -  .  , 


Dorsal  Lamina 


4i6 


EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD. 


The  roof-plate  of  the  diencephalon  stretches  out  and  becomes 
very  thin,  except  at  its  posterior  extremity  (Figs.  ii8,  V3,  and 
120).  Its  major  portion  forms  the  epithehum  covering  the  third 
ventricle.  Posteriorly,  fibers  grow  through  it  from  opposite  sides 
and  form  a  transverse  white  band,  the  posterior  commissure.  Im- 
mediately in  front  of  this  commissure,  a  diverticulum  of  the  roof- 
plate  appears  which  is  the  primitive  pineal  body.  The  pineal 
body  soon  becomes  solid  and  is  joined  to  the  diencephalon  by  a 


cqa 


—? 


Fig.   124. — Dorsal  view  of  an  embryonic  brain,  the  roof  of  the  lateral   ventricles 
having  been  cut  away.     Embryo  of  12.6  mm.     (McMurrich  after  His.)  . 

b.  Brachium  superius.  eg.  Corpus  geniculatum  laterale.  Cp.  Chorioidlfplexus  of  lateral 
ventricle.  Cqa.  Colliculus  superior  of  corpora  quadrigemina.  h.  Hippocampus,  hf.  Hip- 
pocampus and  fissure.     Ot.  Thalamus,     p.  Pineal  body.     rp.  Roof -plate. 

constricted  stalk  in  which  there  is  a  conical  prolongation  of  the 
ventricular  cavity,  called  the  pineal  recess  (Fig.  120).  Anterior 
to  the  pineal  body,  two  longitudinal  folds  of  the  roof -plate  dip 
doA\Ti  into  the  ventricular  cavity.     These  are  followed  by  two 


MESENCEPHALON.  417 

like  downward  projecting  folds  from  the  inferior  lamina  of  the 
chorioid  tela,  which  constitute  the  chorioid  plexuses  of  the  third 
ventricle. 

The  dorsal  lamina  of  the  diencephalon  thickens  greatly  and 
so  encroaches  upon  the  ventricle  as  to  convert  it  into  a  narrow 
median  slit.  Externally,  the  dorsal  lamina  fuses  with  the  cere- 
bral hemisphere,  as  a  result  of  the  formation  of  the  internal  cap- 
sule; and  the  fusion  at  one  point  of  the  medial  surfaces  of  the  two 
dorsal  laminae  g\\Q's>x\'~,Qio{h.Qinassaintermedia  (middle commissure). 
The  development  of  the  thickened  dorsal  lamina  of  the  diencepha- 
lon produces  the  thalamus  with  its  pulvinar  and  the  geniculate 
bodies  (Fig.  124). 

The  ventral  lamina  and  floor-plate  of  the  diencephalon  con- 
stitute the  pars  mammillaris  hypothalami,  which  embraces  some 
gray  and  white  matter  beneath  the  thalamus,  and  the  corpora 
mammillaria  (Fig.  118,  VI).  A  single  oval  eminence  situated 
in  the  median  Kne,  represents  the  mammillary  bodies  up  to  the 
third  month ;  but,  during  the  third  month,  that  eminence  is  divided 
into  the  two  white  bodies  (corpora  albicantia)  of  the  adult.  The 
gray  substance  immediately  in  front  of  the  corpora  mammillaria 
also  belongs  to  this  region,  hence  a  part  of  the  tuber  cinereum  is 
included  among  the  derivatives  of  the  diencephalon. 

MESENCEPHALON. 
This  is  the  mid-brain  (Figs.  17,  118,  IV,  and  120).  It  is  the 
third  of  the  secondary  vesicles.  The  elbow  of  the  mesencephalic 
flexure  of  180  degrees  is  formed  by  it;  and  that  flexure  almost 
brings  the  diencephalon  and  metencephalon  in  contact  with  one 
another  beneath  it.  The  mesencephalon  remains  small,  but  its 
walls  thicken  greatly.  As  a  result  of  the  thickening,  its  cavity 
is  reduced  to  a  slender  canal,  the  cerebral  aqueduct  (Fig.  120).. 

TABLE  VIII. 

DERIVATIVES  OF  MESENCEPHALON. 


Dorsal  Zones 


27 


I  Lamina  quadrigemina 
I       Colliculi 
j       Brachia  (in  part) 
[  Red  nuclei. 


41 8  EMBRYOLOGY    OP    THE    BRAIN   AND    SPINAL    CORD. 


Ventral  Zones  -\ 


Stratum  griseum  centrale  (in  part) 
Nuclei  of  third,  fourth  and  part  of  fifth 

nerve 
Nuclei  laterales  superiores 
I  Tegmenta  (above  isthmus) 
[  Substantia  nigra  (above  isthmus). 


Little  is  known  about  the  development  of  the  mid-brain. 
The  origin  of  the  derivatives  tabulated  above  is  largely  inferred 
from  their  position  and  function.  The  formation  of  the  corpora 
quadrigemina  has  been  observed  (Figs.  120  and  124).  In  the 
dorsal  part  of  the  mesencephalon,  an  elongated  eminence  on  either 
side  of  median  line  is  present  at  the  beginning  of  the  third  month. 
Those  two  eminences  resemble  the  corpora  bigemina  of  birds, 
fishes  and  reptiles.  Two  months  later  a  transverse  groove  divides 
each  eminence  into  the  superior  colliculus  and  the  inferior  collic- 
ulus.  By  the  growth  of  fibers  through  the  marginal  velum  be- 
tween the  colliculi  and  the  corpora  geniculata  the  brachium  supe- 
rius  and  the  brachium  injerius  are  produced  (Fig.  43).  The  bases 
pedunculi  are  produced,  likewise,  by  the  down-growth  of  fibers 
from  the  fore-brain,  which  traverse  the  marginal  velum  in  the 
ventral  region  and,  when  medullated,  form  the  prominent  strands 
of  the  adult. 

METENCEPHALON. 

The  metencephalon  is  the  fourth  of  the  secondary  brain  vesicles. 
From  it  are  derived  the  isthmus,  the  cerebellum  and  the  pons 
(Figs.  17,  118,  III,  and  IV,  and  120).  Its  dorsal  wall,  which  forms 
the  cerebellum,  presents  a  transverse  indentation,  the  metenceph- 
aUc  angle ;  and,  as  a  result  of  that  angle  the  opposite  wall  is  bulged 
forward.  The  ventral  wall  of  the  metencephalon  forms  the  pons. 
The  cavity  of  this  vesicle  forms  the  upper  half  of  the  fourth 
ventricle.  Superiorly,  this  cavity  contracts  to  the  size  of  the  cere- 
bral aqueduct;  it  expands  inferiorly  and  is  broadest  at  the  junc- 
tion of  the  pons  with  the  medulla  oblongata.  The  ventricular 
surface  presents  on  each  lateral  wall  a  longitudinal  furrow  which 
divides  the  metencephalon  into  a  ventral  and  a  dorsal  zone.  In 
the  adult  the  location  of  that  furrow  is  indicated  by  the  sulcus 


METENCEPHALON. 


419 


limitans  of  the  rhomboid  fossa,  containing  the  jovea  superior  and 
the  locus  ccBruleus,  hence,  the  pons  comprises  the  greater  portion 
of  the  metenccphalon,  including  the  entire  ventral  zone  and  a 
part  of  the  dorsal  zone. 


TABLE  IX. 
DERIVATIVES  OF  METENCEPHALON 


Roof-plate 


Metencephalon  Proper 

Inferior  velum 
Cerebellar  vermis 


(McMurrich,  modified). 

Isthmus 

Superior  velum,  or  valve  of 
Vieussens  —  contains  de- 
cussation of  trochlear 
nerves. 


Dorsal  Zones 


Ventral  Zones 


Floor-plate 


f  Lobes  of  cerebellum 
I  Terminal  nuclei,  of  sensory 
J       nerves  (part  of  fifth  and 
eighth) 
Ganglia  of  cerebellum  ( ?) 
Nucleus  pontis  ( ?) 
Genetic    nuclei    of    motor 
nerves   (fifth,   sixth,   sev- 
enth) 
I  Nuclei  centrales  and  nucleus 
I       lateralis  medius  of  the  re- 
[      ticular  formation 

Median  raphe 


Brachium  conjunctivum  of 
cerebellum  grows  through 
it. 


Inferior  part  of  tegmen- 
tum and  of  substantia 
nigra. 

The  basis  pedunculi  grows 
down  through  it. 


Median  raphe. 


Cerebellum. — ^It  forms  the  roof  of  the  upper  part  of  the  fourth 
ventricle,  that  is  as  far  down,  as  the  transverse  fold  of  invaginated 
roof-plate,  called  the  plica  chorioidea,  produced  by  the  meten- 
cephalic  flexure  (Fig.  118,  between  II  and  I).  Above  the  plica 
chorioidea  the  dorsal  laminae  of  the  metencephalon  thicken 
rapidly  and  form  a  prominent  transverse  ridge  on  either  side  of 
the  median  line.  The  two  thickenings  are  partially  separated 
from  each  other  in  the  median  line  by  a  deep  ventricular  sulcus 
but  joined  dorsally  by  a  thin  bridge  of  tissue,  the  metencephahc 
roof-plate.  At  this  early  stage  there  is  no  representative  of  the 
vermis  cerebelli,  the  ridges  represent  the  hemispheres.  But 
very  soon,  cells  from  the  dorsal  laminae  invade  and  thicken  the 


420  EMBRYOLOGY   OF    THE    BRAIN   AND    SPINAL    CORD. 

roof -plate  to  the  extent  of  obliterating  the  median  ventricular  sulcus 
and  completely  uniting  the  two  dorsal  laminae.  The  cerebellum 
is  now  represented  by  one  continuous  transverse  ridge  arching 
over  the  fourth  ventricle.  It  develops  slowly  in  comparison  with 
the  cerebrum.  The  lateral  parts  develop  more  rapidly  than  the 
median  portion  after  the  third  month.  Thus  the  hemispheres 
are  differentiated  from  the  vermis.  The  flocculus  is  the  first 
lobule  to  be  formed  and  it  reaches  a  high  development  in  the  third 
month;  other  lobules  of  the  hemisphere  which  are  more  charac- 
teristic of  the  human  cerebellum,  the  tonsil,  the  quadrangular 
lobe,  the  superior  semilunar  and  the  inferior  semilunar  lobules, 
are  not  fully  formed  until  near  birth.  The  folium  vermis  of  the 
worm  is  developed  after  birth  (Figs.  76  and  80). 

Sulci  (Fig.  79). — ^The  chief  sulci  of  the  worm  appear  in  the 
third  month;  with  two  exceptions,  those  of  the  hemisphere  de- 
velop later.  The  lateral  part  of  the  postnodular  sulcus  is  first 
manifest.  In  the  second  month  it  cuts  off  a  strip  of  the  cerebellar 
ridge,  just  above  the  chorioidal  plica,  which  is  the  primitive  floc- 
culus. A  little  later  the  sulcus  extends  across  the  median  line 
and  forms  the  posterior  boundary  of  the  nodule.  The  next  sul- 
cus to  develop  is  ^ the  predeclivil  sulcus  (Fig.  79).  It  cuts  very 
deeply  into  the  vermis  between  the  culmen  and  the  declive.  From 
the  vermis  it  extends  into  the  hemispheres,  where  it  separates 
the  anterior  and  the  posterior  parts  of  the  quadrangular  lobe. 
The  prepyramidal  and  the  postpyramidal  sulci  are  formed  near 
the  end  of  the  third  month  (Fig.  79).  In  the  fourth  month  the 
hemispheral  part  of  the  postdeclivil  sulcus  is  first  visible  behind 
the  quadrangular  lobule  (Fig.  76).  Soon  it  becomes  continuous 
through  the  vermis  with  that  of  the  opposite  hemisphere.  It  is 
the  beginning  of  the  fifth  month  before  the  prepyramidal  sulcus 
is  extended  into  the  hemisphere  between  the  tonsil  and  biventral 
lobule  (Fig.  80).  At  about  the  same  time  the  lateral  extension  of 
the  postpyramidal  sulcus  establishes  the  posterior  boundary  of 
the  biventral  lobule.  According  to  O.  C.  Bradley's  study  of  the 
rabbit's  cerebellum,  the  postcentral  sulcus  and  the  precentral  sul- 
cus appear  at  about  the  same  time  as  the  postdeclivil.  The  last 
important    sulcus    to|[appear|[is   the  horizontal  sulcus   (Figs.   76 


METENCEPHALON.  421 

and  80).  It  is  not  well  formed  until  near  birth  and  is  produced 
almost  wholly  by  the  enormous  growth  of  the  superior  and  the 
inferior  semilunar  lobules  which  are  so  characteristic  of  the  human 
cerebellum  (Cunningham). 

The  cerebellar  lobules  are  subdi^•ided  into  gyvi  by  intralobular 
sulci  which  develop  in  the  later  months  of  pregnancy  and  the  early 
months  of  extrauterine  life.  There  are  two,  called  the  midgra- 
cile  and  postgracile  sulci,  which  Bradley  says  are  found  only  in 
man  and  the  anthropoid  apes. 

Cortex  and  Ganglia. — ^Little  is  kno^^^l  of  the  particular  order 
and  manner  of  development  in  either  the  cortex  or  ganglia  of  the 
cerebellum.  As  to  the  cortex,  it  consists  in  general,  (i)  of  the 
multiplication  and  development  of  the  cells  in  the  mantle  layer, 
some  of  whose  processes  descend  to  the  cerebellar  gangha  and 
Deiters's  nucleus,  and,  (2)  of  the  formation  of  contacts  with  in- 
growing fibers  from  pons,  medulla  and  spinal  cord. 

Corpus  Restijorme  of  Cerebellum. — ^Fibers  from  the  cerebellar 
cortex  descending  to  the  medulla,  and  ascending  fibers  from  the 
cord  and  medulla  in  their  course  to  the  cerebellar  cortex,  give 
rise  to  the  corpus  restijorme  in  the  third  month.  Fibers  from 
the  nucleus  pontis  and  nucleus  fastigii  form  the  brachium  pontis 
a  month  later  and  in  the  fifth  month  the  brachium  conjunctivum 
is  produced  by  fibers  from  the  nucleus  dentatus. 

Pons  (Figs.  118,  II,  I,  121  and  122). — ^The  pons  develops  sim- 
ultaneously with  the  cerebellum.  The  ventral  zone  of  the  met- 
encephalon  thickens  greatly.  The  neuroblasts  formed  therein 
constitute  the  nuclei  of  the  pons  (?)  and  of  the  reticular  jonnation, 
and  the  motor  nuclei  for  the  'jijth,  sixth  and  seventh  pairs  of  cere- 
bral nerves;  the  dorsal  lamina  in  the  lateral  wall  of  the  meten- 
cephalon,  produces  the  neuroblasts  which  form  the  superior  olivary 
nucleus  and  the  superior  part  of  the  terminal  nucleus  of  the  trigem- 
inal and  of  the  acustic  nerve.  From  the  nucleus  pontis  axones 
ascend  through  the  lateral  walls  of  the  metencephalon  to  the  cere- 
bellunj.  They  form  most  of  the  brachia  pontis.  At  the  same 
time,  about  the  fourth  month,  the  motor  tracts  composing  the 
basis  pedunculi  grow  do\Miward  into  the  ventral  portion  of  the 
pons  and  the  jronto-pontaU  tern poro-pontal  and  intermediate  tracts 


422 


EMBRYOLOGY   OF    THE    BRAIN   AND    SPINAL    CORD. 


end  in  the  nuclei  pontis.  The  pyramidal  -fibers  to  motor  nuclei  of 
spinal  nerves  grow  down  through  the  pons,  intersecting  its  trans- 
verse fibers. 

MYELENCEPHALON. 

The  myelencephalon  forms  the  medulla  oblongata  (Figs.  ii8, 
I,  and  122).  It  is  constricted  off  from  the  metencephalon  at  the 
twenty-eighth  day;  but,  later,  that  constriction  largely  disappears 
and  the  common  cavity  of  the  two  vesicles,  broad  in  the  middle 


Fig.  125. — Transverse  section  of  medulla  from  an  embryo  of  91.  mm.     (McMur- 

rich  after  His.) 

dz.  Dorsal  zone.    fp.  Floor -plate,    fs.  Tractus  solitarius.    I.  Lip.    rp.  Roof -plate,    vz.  Ven- 
tral zone.    X  and  XII.  Tenth  and  twelfth  nerves. 


and  contracted  to  a  slender  canal  at  each  end,  persists  as  the 
fourth  ventricle  of  the  mature  brain.  Like  the  metencephalon, 
the  fifth  brain  vesicle  is  divided  at  the  third  week  into  a  ventral 
and  a  dorsal  zone  by  a  deep  furrow  on  the  ventricular  surface  of  each 
lateral  wall  (Figs.  125  and  126).  That  lateral  furrow  actually  per- 
sists in  the  sulcus  limitans  and  inferior  fovea  of  the  fourth  ventricle. 
The  roof-plate  of  the  superior  half  of  the  myelencephalon  stretches 
out  widely  and  remains  a  single  layer  of  epithelial  cells.  It  forms 
no  nerve  tissue.  Other  portions  of  the  myelencephalon  develop 
quite  uniformly.  But  by  the  expansion  of  the  roof,  just  mentioned, 
the  dorsal  extremities  of  the  lateral  walls  are  pushed  outward  and 


MYELENCEPHALON. 


423 


forward  almost  to  the  plane  of  the  floor,  and  a  transverse  section 
of  the  vesicle  in  that  region  presents  the  form  of  a  very  broad 
capital  V  with  the  roof  epithelium  stretching  between  the  two 
arms  and  converting  the  letter  into  a  triangle.  Transverse  sec- 
tion through  the  lower  half  of  the  myelencephalon  at  the  third 
or  fourth  week  shows  an  elongated  ellipse  with  a  dorso-ventral 
major  axis. 

Internal  Surface  (Fig.  125). — ^The  lateral  wall,  in  both  upper 
and  lower  regions,  presents  the  longitudinal  groove  which  sepa- 
rates the  ventral  and  dorsal  zones.  The  median  ventral  groove 
persists  throughout  and  the  lateral  grooves  are  represented  by  the 


Fig.  126. — Transverse  section  of  the  medulla  from  an  embryo  of  eight  weeks. 
{McMurrich  after  His.) 

av.  Spinal  tract  of  the  trigeminal  nerve,    fr.  Substantia  reticularis.    01.  Olivary  nucleus 
of  medulla,    sf.  Tractus  solitarius.    tr.  Restif orm  body.    XII.  Hypoglossal  nerve. 


sulcus  limitans  and  inferior  fovea  of  the  fourth  ventricle  (Fig.  96). 
The  low  eminence  situated  between  the  median  and  each  lateral 
groove  becomes  the  eminentia  medialis. 

External  Surface  (Figs.  125  and  126). — On  the  exterior  sur- 
face of  the  myelencephalon,  along  the  ventral  border  of  the 
dorsal  zone,  there  appears  very  early  an  oval  bundle  of  de- 
scending fibers,  called  the  solitary  tract.  It  is  composed  of 
axones  from  the  geniculate,  glossophar\Tigeal  and  vagus  gan- 
glia, and  constitutes  the  root-fibers  of  the  intermediate,  the  ninth 
and  tenth  pairs  of  nerves.  At  about  the  same  time  axones 
from    the    semilunar    ganglion    form    a  bundle   of    descending 


424 


EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD. 


fibers  on  the  lateral  surface  ventral  to  the  solitary  tract.  They 
constitute  the  spinal  tract  of  the  trigeminal  nerve.  Soon  after  the 
appearance  of  the  solitary  tract  and  the  spinal  tract  of  the  fifth 
nerve,  the  posterior  margin  of  the  dorsal  lamina  is  folded  out- 
ward and  forward  until  it  rests  upon  the.  external  surface.  That 
fold,  which  is  called  the  rhombic  lip,  covers  both  the  above  bundles 
of  fibers  and  places  them  in  the  position  they  occupy  in  the  mature 
brain.  Between  the  rhombic  lips  the  roof  epithelium  stretches 
across  the  ventricle  and  pushes  a  transverse  fold  into  it.  The 
mesoblast  which  dips  into  that  fold  develops  the  chorioid  plexus 
of  the  fourth  ventricle  (Fig.  91). 

TABLE  X. 


DERIVATIVES  OF  MYELENCEPHALON. 

(Modified  from  McMurrich.) 


Roof-plate 


Dorsal  Zone 


Ventral  Zone 


Surrounding  Mesoblast 


Roof  epithelium 

Nuclei  funiculi  —  gracilis,  and  cuneati, 
and  nucleus  tractus  spinalis  n.  tri- 
gemini. 

Olivary  nuclei  (inferior) 
-\  Arcuate  nuclei 

Terminal  nuclei  of  sensory  roots  of  cere- 
bral nerves  (intermediate,  eighth,  ninth 
and  tenth) 

Sensory  tracts  grow  up  through  it. 

['  Nucleus  lateralis  inferior 
Genetic  nuclei  of  motor  roots  and  nerves, 

ninth,  tenth  and  eleventh  (its  bulbar 

root)  and  twelfth 
Motor  tract   (pyramid)   grows   down 

through  it. 

Meninges — 

Chorioid  plexus  of  fourth  ventricle. 


The  substance  of  the  myelenceplialon,  hke  other  divisions 
of  the  neural  tube,  presents  under  the  microscope  three  distinct 
layers  at  the  fourth  week  of  embryonic  Hfe   (Fig.   125).     The 


MYELENCEPHALON.  425 

outer  layer,  the  marginal  velum,  is  composed  of  neuroglia;  the 
middle,  or  marille  layer,  of  neuroblasts;  and  the  inner,  or  ependy- 
mal  layer  is  made  up  of  columnar  epithelial  cells. 

The  cells  of  the  inner  layer  become  ciliated  and  fonn  the  lining 
of  the  ventricle. 

The  mantle,  or  middle  layer  undergoes  most  development. 
Its  neuroblasts  form  the  substantia  reticularis  and  the  cerebral 
nerve  nuclei  and  other  nuclei  of  the  medulla  oblongata.  In  the 
dorsal  zone  the  neuroblasts  form  the  terminal  nuclei  for  the  eighth, 
ninth  and  tenth  cerebral  nerves  and  the  nucleus  funiculi  graciUs, 
nucleus  funicuU  cuneati  and  nucleus  of  the  spinal  tract  of  the  tri- 
geminal nerve.  As  early  as  the  fourth  week  axones  may  be  traced 
from  the  nucleus  funicuH  graciUs  and  nucleus  funicuH  cuneati, 
ventro-medially,  toward  the  point  where  they  very  soon  form  the 
fillet  decussation.  Neuroblasts  which  have  wandered  from  the  dor- 
sal zone  form  the  arcuate,  the  olivary  and  accessory  olivary  nuclei. 
The  oUvary  nuclei  are  developed  quite  late  in  the  intrauterine 
life  (sixth  month).  The  nucleus  of  the  cuneate  funiculus,  the 
nucleus  of  the  spinal  tract  of  the  n.  trigeminus,  the  oHvarv^  and 
arcuate  nuclei  are  all  products  of  the  rhombic  lip  (Cunningham). 
From  the  neuroblasts  of  the  ventral  zone  are  developed  the  gray 
matter  and  fibers  of  the  substantia  reticularis  alba  et  grisea,  and 
the  motor  nuclei  of  the  twelfth,  eleventh  (cerebral  part),  tenth 
and  ninth  pairs  of  cerebral  nerves. 

The  neuroglia  layer,  or  marginal  velum,  forms  the  support- 
ing matrix  for  the  tracts  of  fibers  in  the  medulla.  By  the  third 
month  the  funiculus  gracihs  and  funiculus  cuneatus,  extensions 
of  the  same  fascicuh  in  the  cord,  have  gro\Mi  up  to  their  terminal 
nuclei  in  the  medulla.  The  restiform  body  is  at  that  time  well 
developed,  and  the  tracts  of  the  lateral  area  of  the  medulla  are 
visible.  The  medial  longitudinal  bundles  appear  near  the  median 
raphe  in  the  ventral  zone  at  about  the  same  time;  and,  ventral  to 
them,  fibers  from  the  fillet  decussation  insinuate  themselves  and 
form  the  interohvary  stratum  of  the  medial  fillets.  The  great 
motor  tracts  from  the  anterior  central  gyrus  of  the  cortex  reach 
the  medulla  at  the  fourth  month.  Growing  downward  in  the 
neurogHa  layer,  on  either  side  of  the  median  line,  they  conceal  the 


426  EMBRYOLOGY    OF   THE    BRAIN   AND    SPINAL    CORD. 

medial  fillets  and  form  the  pyramids  of  the  medulla  oblongata. 
The  form  of  the  medulla  is  completed  two  months  later  (the  sixth 
month)  by  the  appearance  of  the  olivary  bodies  (Fig.  93). 

SPINAL  CORD. 

That  portion  of  the  neural  tube  which  is  situated  behind  the 
metencephalon  is  the  embryonic  spinal  cord  (Figs.  16  and  118). 
It  is  of  nearly  uniform  size  from  cephahc  to  caudal  end.  The 
lumen  of  the  neural  tube  in  this  region  is  at  first  large  and  ellip- 
tical in  shape.  Later,  at  the  sixth  week,  it  has  a  diamond  shape, 
the  acute  angles  of  the  diamond  being  formed  by  the  roof-plate 
and  floor-plate  of  the  canal;  it  is  lined  with  columnar  ciliated 
cells  (Fig.  117).  As  the  walls  thicken  the  canal  is  contracted 
more  and  more  until  it  reaches  the  capillary  size  of  the  adult  cord. 
The  canal  is  continuous  with  the  fourth  ventricle  above  and  dilates 
to  form  the  ventriculus  terminalis  in  the  filum  terminale  internum 
(Fig.  no).  The  spinal  part  of  the  neural  tube  forms  the  whole 
substance  of  the  spinal  cord,  with  the  exception  of  the  great  motor 
tracts  that  grow  into  it  from  the  brain,  and  the  sensory  tracts  and 
fibers  that  enter  it  from  the  spinal  ganglia.  At  the  sixth  week 
of  embryonic  life  the  anterior  and  posterior  roots  of  the  spinal 
nerves  are  clearly  seen;  they  are  horizontal  in  direction.  The 
cord  extends  to  the  fourth  mesoblastic  somite  of  the  coccyx,  when 
the  somites  are  first  laid  down;  but,  as  no  neuroblasts  are  developed 
by  the  three  lower  segments  of  the  human  cord,  they  form  a  con- 
nective tissue  strand,  the  primitive  -filum  terminale  (McMurrich). 
The  cord  occupies  the  entire  length  of  the  spinal  canal  until  the  third 
month,  when  the  caudal  end  begins  to  recede  and  the  filum  ter- 
minale to  lengthen.  It  reaches  only  to  the  third  lumbar  verte- 
bra at  birth  and,  in  the  adult,  but  to  the  lower  border  of  the  first 
lumbar  vertebra.  With  the  rapid  growth  of  the  spinal  column, 
the  roots  of  the  lumbar,  sacral  and  coccygeal  nerves  and  the  filum 
terminale  become  greatly  elongated  and  form  the  cauda  equina. 

Meninges. — ^The  investing  mesoblast  of  the  neural  tube  devel- 
ops the  meninges  of  the  spinal  cord. 

Zones  (Figs.  117  and  127A). — ^By  the  sixth  week  of  intrauterine 


SPINAL    CORD. 


427 


life  the  neural  tube,  in  the  spinal  region,  is  divided  into  a  ventral 
and  a  dorsal  zone  by  a  lateral  groove  on  either  side,  continuous 
with  that  formed  in  the  rhombencephalon  two  weeks  earlier. 
The  tube  presents  externally,  opposite  to  each  lateral  groove, 
a  furrow  in  the  mantle  layer  representing  the  concavity  of  the 
gray  crescent  and  called  the  central  fissure;  it  is  occupied  later 
by  the  lateral  pyramidal  and  other  tracts.  The  whole  of  the  spinal 
cord  ventral  to  the  bases  of  the  posterior  columnar  of  gray  matter 
is  represented  by  the  ventral  zones.     From  them  grow  out  the 


mm 


LVz 


Fig.  127. — Transverse  sections  through  the  spinal  cords  of  embryos  of  (A)  about 
four  and  a  half  weeks  and  (B)  about  three  months.     {McMiirrich  after  His.) 

cB.  Fasciculus  cuneatus  (Burdachi).  cG.  Fasciculus  gracilis  (Golli).  dh.  Posterior 
columna.  dz.  Dorsal  zone.  fp.  Floor-plate,  ob.  Oval  bundle  (Hisi).  rp.  Roof-plate. 
vh.  Anterior  columna.     vs.  Ventral  zone. 


anterior  roots  of  the  spinal  nerves.  In  the  dorsal  zones  the  pos- 
terior columnee  and  the  posterior  columns  of  fibers  are  developed. 
They  receive  the  posterior  roots  of  the  spinal  nerves  (Figs.  117, 
127   and   128). 

Three  Histologic  Layers  (Figs.  116  and  127A). — ^At  a  time 
somewhat  earher  than  the  division  into  ventral  and  dorsal  zones, 
even  at  the  fourth  or  fifth  week,  the  spinal  part  of  the  neural  tube 


428 


EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD. 


presents  three  microscopic  layers,  like  those  seen  earlier  in  the 
brain  vesicles. 

The  outer  layer,  or  marginal  velum,  composed  of  neuroglia, 
is  very  thin  except  in  the  central  fissure  and  in  the  floor  and  roof 
of  the  tube  on  either  side  of  the  median  line.  In  those  situations 
are  formed  the  lateral,  the  anterior  and  the  posterior  funiculi  of 
the  cord. 

The  mantle  layer  is  gray  matter.  It  contains  the  neuro- 
blasts. At  the  fourth  or  sixth  week  it  is  very  thick,  comprising 
nearly  all  of  the  neural  tube.     The  H-shaped  column  of  gray  sub- 


Pdstenor 
Jloot 


Intertor 
Jiooi 


Fig.  128. — Mode  of  origin  of  anterior  and  posterior  roots  of  spinal  nerves.  Diagram- 
inatic.     {Brubaker  and  Edinger  after  His.) 


Stance  is  derived  from  this  layer.  In  the  ventral  zone  the  neuro- 
blasts develop  earhest.  They  collect  near  the  floor  of  the  tube 
and  form  a  large  column  on  either  side  of  the  median  line,  the  an- 
terior columna.  The  axones  of  the  more  ventrally  located  neuro- 
blasts grow  centrifugally  out  of  the  antero-lateral  surface  of  the 
neural  tube.  They  form  the  anterior  roots  of  the  spinal  nerves. 
The  more  dorsally  located  neuroblasts  develop  axones  also;  but 
on  account,  of  meeting  resistance,  according  to  His,  they  become 
longitudinal  and  form  the  fasciculi  proprii  of  the  cord  and,  per- 
haps, the  ascending  anterior  cerebello-spinal  and  the  spino-thala- 


SPINAL    CORD.  429 

mic  tracts.  The  gray  matter  in  the  dorsal  zone  develops  later. 
It  becomes  transformed  into  the  posterior  columna;  its  neurobhists 
form  largely  intrinsic  neurones,  their  processes  remaining  in  the 
spinal  cord,  others  give  rise  to  the  posterior  cerebeUo-spinal 
tract  which  ascends  through  the  marginal  velum  to  the  vermis 
superior  of  the  cerebellum.  Axones  from  the  spinal  ganglia, 
forming  the  posterior  roots  of  the  spinal  nerves,  grow  into  the  dor- 
sal zone;  and  each  axone  divides  T-Hke  into  a  descending  and  an 
ascending  branch,  and  also  gives  off  many  collaterals  both  before 
and  after  division.  The  ascending  fibers  for  a  time  form  the 
oval  bundle  of  His  on  the  surface  of  the  tube;  later,  they  constitute 
the  marginal  tract  (Lissaueri)  and  the  fasciculus  cuneatus  (Burd- 
achi)  and  fasciculus  gracilis  (Golli). 

The  third,  or  ependymal  layer,  lines  the  ventricle.  It  is  com- 
posed of  neuroglia  covered  internally  by  columnar  ciliated  cells, 
which  appear  about  the  fifth  week. 

The  Longitudinal  Tracts  (Figs.  loi,  102  and  103). — ^The  white 
columns  of  the  spinal  cord  are  formed  in  the  superficial,  or  neu- 
roglia layer.  At  first  they  are  composed  of  nonmedullated  libers, 
and  it  is  a  remarkable  fact  that  the  various  tracts  receive  their 
myelin  sheaths  at  definite  periods  between  the  fifth  and  ninth 
months  of  intrauterine  Hfe  (Flechsig).  The  anterior  nerve- 
roots  and  the  anterior  and  lateral  fasciculi  proprii,  and  the  pos- 
terior nerve-roots  and  the  oval  bundles  of  His  are  first  to  make 
their  appearance.  The  axones  of  these  nerves-roots  and  tracts 
may  be  seen  at  the  sixth  week.  The  ascending  cerebeUo-spinal 
tracts  follow,  and  the  descending  cerebello-spinal  and  the  pyram- 
idal tracts  are  last  to  appear;  they  are  not  developed  before  the 
fourth  or  fifth  month.  According  to  Kahler,  as  quoted  by  Cun- 
ningham, the  tracts  of  the  spinal  cord  are  medullatcd  as  follows : 

1.  Fibers  of  the  fasciculus  cuneatus  with  the  posterior  nerve- 
roots,  preceded  by  the  medullation  of  the  anterior  nerve-roots 
(fifth  month). 

2.  Fibers  of  anterior  and  lateral  fasciculi  proprii  (fifth  and 
sixth  months). 

3.  Fibers  of  fasciculus  gracihs  (sixth  month). 

4.  Posterior  cerebello-spinal  tract  (seventh  month). 


43©  EMBRYOLOGY    OF    THE    BRAIN   AND    SPINAL    CORD. 

5.  Ascending  anterior  cerebello-spinal  and  spino-thalamic  tracts 

(?)  (eighth  month). 

6.  Pyramidal  tracts  (ninth  month). 

Fissures  (Fig.  loi). — ^The  so-called  posterior  median  -fissure 
is  in  reality  a  septum  of  neuroglia.  At  no  time  is  it  a  true  fissure. 
Its  mode  of  formation  is  still  in  doubt.  It  appears  to  be  pro- 
duced by  thickening  in  the  roof-plate  due  to  the  elongation  of 
ependymal  cells.  From  the  sixth  week  this  neuroglia  septum  ex- 
tends ventrally  until  it  reaches  the  center  of  the  cord. 

The  posterior  lateral  sulcus  is  the  groove  between  the  lateral 
border  of  the  posterior  column  and  the  dorsal  border  of  the 
lateral  column.  It  is  the  development  of  the  posterior  and  lateral 
columns  that  produces  the  fissure.  The  embryonic  central  fis- 
sure is  obhterated  and  the  postero-lateral  surface  of  the  cord  ren- 
dered prominent  by  the  formation  of  the  lateral  fasciculus  proprius, 
the  cerebello-spinal  and  the  pyramidal  tracts. 

Anterior  Median  Fissure. — ^That  is  a  true  fissure.  It  begins 
to  be  formed  at  the  sixth  week,  when  the  anterior  columnae  and 
the  earliest  fibers  of  the  anterior  fasciculus  proprius  are  developing. 
It  deepens  with  the  growth  of  the  gray  columnae  and  of  the 
anterior  fasciculus,  proprius  and  its  walls  are  further  heightened, 
in  the  fourth  or  fifth  month,  by  the  descent  of  the  anterior  pyr- 
amidal tracts.  In  this  manner  there  is  produced  a  bulging  of  the 
anterior  surface  on  either  side  of  the  median  line,  which  increases 
with  the  meduUation  of  the  longitudinal  tracts  up  to  the  ninth 
month.  The  ridges  thus  produced,  failing  to  fuse  completely, 
become  the  walls  of  the  anterior  median  fissure.  The  partial 
fusion  which  does  occur  between  the  two  ridges  is  due  to  the  for- 
mation of  the  white  anterior  commissure  of  the  cord. 


ADDENDA. 


According  to  Head,  Rivers  and  Sherren  (Brain,  1905)  three 
distinct  mechanisms  operate  in  the  production  of  common  sensa- 
tion, one  concerned  vnih  deep  sensibiHty  and  two  with  superficial 
sensibility.  The  mechanism  of  deep  sensibility  includes  the  ners^es 
supplying  muscles,  tendons,  joints  and  ligaments.  Though  it 
may  be  affected  by  en\ironment,  it  is  chiefly  acted  upon  by  stimuli 
originating  wdthin  the  organism,  such  as  pressure  (resulting  from 
weight  and  inertia)  and  tension.  It  may  give  rise  to  painful 
sensations,  but  its  principal  concern  is  with  muscular  tonicity 
and  equiHbrium.  The  nerves  of  the  deep  mechanism  constitute 
the  "proprio-ceptors"  of  Sherrington.  They  are  so  named  be- 
cause their  stimuh  are  furnished  chiefly  by  the  organism  itself 
(Brain,  1906).  The  mechanisms  of  superficial  (cutaneous)  sen- 
sibility are  called  by  Head,  Rivers  and  Sherren  the  Protopathic 
and  the  Epicritic.  The  protopathic  mechanism  responds  to  pain- 
ful cutaneous  stimuH  and  to  extremes  of  heat  and  cold.  It  may 
set  up  reflexes  without  arousing  consciousness.  Cutaneous  local- 
ization is  no  part  of  its  function.  The  mechanism  of  epicritic 
sensibility  is  adapted  to  mild  stimuli,  to  light  touch,  to  warmth, 
to  coolness.  By  it  the  localization  of  cutaneous  stimuU  is  acconi- 
pHshed  and  its  activity  usually  involves  consciousness.  It  may 
also  produce  reflexes  through  the  efferent  nerves.  Sherrington 
speaks  of  these  two  mechanisms  as  the  "extero-ceptors"  and 
gives  the  name  "intero-ceptors"  to  the  nerves  of  the  interior  sur- 
faces, those  of  the  alimentary  tract,  etc.  The  "intero-ceptors" 
are  especially  adapted  to  chemical  stimuH  and  give  rise  to  diges- 
tive reflexes;  but  they  may  also  produce  pain  and  temperature 
sensations,  and  may  respond  to  stimuli  occasioned  by  tension  and 
pressure.     See  pages  365  and  377. 


431 


INDEX 


Abducent  nerve,  45,  153,  321 
Accessory  lemniscus,  227 

nen-e,  5,  49,  153,  293,  322 

nucleus  funiculi  cuneati,  311 
Acustic  center,  181 

nerye,_46,  153,  209,  320 

radiation,    100,    104,    217,   226, 
232,  233,  310 
Acustico-cerebellar  tract,  264 
Afferent  neurone,  171 

paths,  377 

root,  363 

sympathetic  fibers,  348 
After-brain,  ^7, 

Ala  cinerea,  149,  270,  290,  317 
Alveus.  200,  201 
Amygdala,  123,  124 
Angular  g}Tus,_43,  61,  63,  67 
Ansa  lenticularis,  too,  145 

peduncularis,  145,  212 
Anterior  area  of  medulla,  293 

association  center,  182 

brain  vesicle,  30 

calcarine  fissure,  89 

central  gyrus,  39,  59,  60,  61 

central  arterj-,  331 

cerebral  artery,  4,  6,  15,  16,  25 
vein,  23 

chorioidal  artery,  15,  18,  19 

communicating  artery,  14,  15,16 

commissure  of  cerebrum,  30,  95, 
109,131,136,137,234,235, 

411,  413 
columna,  335,  339,  399,  427, 
428 

neurones,  165,  340 
external  arcuate  libers,  292,  295, 

297 
fasciculus  proprius,  354 
horn  of  lateral  ventricle,  120,  137, 

209,  235 
inferior  cerebellar  artery,  15,  27, 

29 
internal  frontal  arteries,  16 


Anterior  lateral  sulcus  of  cord,  335, 

338 
lateral  sulcus  of  medulla,  41,  153, 

295 

longitudinal    bundle,    15S,    161, 
163,219,276,295,297,305, 

341,  345,  355 

median  fissure  of  cord,  335,  337, 

349,  430 
median    fissure  of   medulla,  41, 

285,  286,  295,  337 
median  v'ein  of  medulla,  24 
orbital  g}'rus,  74 
parolfactory  sulcus,  86 
perforated  substance,  ^8,  47,  79, 

207,  235,  267 
pyramidal  tract,  289,  294,  341, 

345,   353 
radicular  artery,  331 
root-line,  335,  338 
root  of  spinal  ner\-e,  327,  334, 

349,  3^3'  399,  427.  428 
slender  lobule,  252,  253,  256 
spinal  artery,  5,  15,  24,  27,  330, 

331 

subarachnoid  space,  8,  327,  329 
surface  of  medulla,  267,  2S6 

of  mid-brain,  267 

of  pons,  266,  267 
temporal  arter\',  19 
tubercle  of  thalamus,  140.  149, 

243 

xAntero-lateral  ganglionic  arteries,  15, 
18,  19,  22 
fasciculus  proprius,  354 
median   ganglionic  arteries,    18, 

Apertura   mediana   ventriculi   quarli 

(Magendi),  9,  290 
lateralis   ventriculi   quarti    (Key 

and  Retzii),  9,  290 
Aqueduct  of  cerebrum,  37 
Aqueductus  cerebri,  37,75,152,  161, 

270 


28 


433 


434 


INDEX. 


Arachnoid  granulations,  5,  6,  65 
of  brain,  8,  9 
of  cord,  326,  327,  329 
Arachnoid  of  brain  and  cord  com- 
pared, 9 
Arachnoidea  encephah,  8 

spiiiah's,  326 
Arbor  vitse,  247,  262 
Archipalhum,  98 
Arcuate  fibers,  291 

nucleus  of  medulla,  295,  297, 

302 
nucleus  of  thalamus,  211 
Arcus  occipito-parietalis,  64,  69 
Area  acustica,  149,  270,  290,  318 
parolfactoria    (Brocse),  47,    75, 

91,  94,  200 
postrema,  270,  318 
for  educated  movements  of  cere- 
brum, 178 
Arteria  basilaris,  14 

carotis  interna,  14,  25 
cerebelli  inferior  anterior,  27,  29 
inferior  posterior,  27,  29 
superior,  27 
cerebri  anterior,  16,  25 
media,  16 
posterior,  17,  25 
chorioidea  anterior,  18 
communicans  an,terior,  14,  25 

posterior,  14,  25 
meningea  media,  6,  7 
spinalis  anterior,  24,  27,  330 

posterior,  24,  27,  330 
vertebralis,  14,  27 
Arteriae  chorioideae  posteriores,  17 

pontales,  24 
Arterial  circle,  14 
Arteries  of  dura,  6 
of  pia  mater,  10 
of  spinal  cord,  330,  331 
Artery  of  cerebral  hemorrhage  (Char- 
cot), 18 
Ascending    anterior    cerebello-spinal 
tract,    287,  295,  297,  298, 

305,  311,  341,  345,  356 

anterior  ramus  of  lateral  fissure 

of  cerebrum,  57 
frontal  arteries,  16,  19,  22 
parietal  arteries,  17,  19,  22 
part     of     medial     longitudinal 

bundle,  157 
postero-medial  tract,  360 


Ascending  postero -lateral  tract,  361 

tracts  of  spinal  cord,  352 
Association  fibers  of  cerebellum,  262, 
265 

fibers  of  cerebrum,  224,  236 
Meynert,  192 
Associative  centers  of  Flechsig,  182 
Atypical  cortex,  192 

neurones,  191 
Auditory  artery,  5 

center,  70,  71 

conduction  path,  160 

paths,  280,  385 
Auditory  and  facial  nerve,  5 
Aula    of    third    ventricle,    30,    137, 

141 
Axones,  168,  169,  398,  400 
Axone  hillock,  167,  169 
Axis  cylinders,  168,  169 

Baillargic  line  (Gennari),  188 
zone  of  cerebral  cortex,  184 

Bandalette  of  Hoche,  345,  362 

Base  of  brain,  36 

of  cerebral  hemisphere,  73,  75 
of  fore-brain,  52,  73,  75 

Basilar  artery,  5,  14,  15 
plexus,  4,  5 
vein,  23 

Basis  pedunculi,  4,  30,  38,  47,  75, 
115,  145,  146,  147.  153, 
157,  159,  161,  418 

Basket  cells  of  cerebellar  cortex,  257, 

259 

Bechterew's  accessory  lemniscus,  227 
superior  nucleus,  277,  280,  308 
Betz,  giant  pyramids  of,  188 
Bipolar  neurones,  400,  401 
Biventral  lobules,  252,  254,  255 
Blood  supply  of  brain,  14 
of  cerebellum,  27 
of  cerebrum,  14 
of  medulla  oblongata,  24 
of  pons  varolii,  24 
of  spinal  cord,  330 
Body  of  fornix,  loi,  109 
Boundaries  of  fourth  ventricle,  313, 
Brachia  of  corpora  quadrigemina,  30, 

146,  164 
Brachium  conjunctivum  cerebelli  (or 
brachia     conjunctiva),     13, 
146,  149, 162,  231,  245,  246, 
252,  261,  263,  275,  289 


INDEX. 


435 


Brachium  inferius  of  orpora  quadri- 
gemina, 

146,  147,  149, 163,  164,  418 
pontis,   13,  41,  149,  209,  245, 
246,    247,    252,  255,  264, 
267, 289 
superius  of  corpora  quadrigem- 
ina,    147,    157,    163,    164, 
207,  416,  418 
Brain,  31 

general  considerations,  34 
vesicles,  30,  34,  3Q5,  402,  403 
Bruce    and    jNIuir's    septo -marginal 

tract,  361 
Bulb    of    posterior    horn    of    lateral 

ventricle,  123,   131 
Bulbus  olfactorius,  77 
Burdach's  column,  300,  361 
Buried  gyrus,  64 

Cajal's    moss-like   appendages,    260, 

259 

tassel  cells,  199 
Calamus  scriptorius,  149,  317 
Calcar  avis,    123,    125,    131,   133, 

410 
Calcarine  artery,  17 

fissure,  43,  75,  86,  89,  91,  95, 

121,  409,  411 
Calleja's  olfactory  islets,  199 
Callosal  sulcus,  80,  86,  91,  95,  loi, 

410 
Calloso-marginal  sulcus,  86 
Canalis  centralis  spinalis,  337 
Capsula  interna,  99 
Cauda  equina,  ^^^.  334 
Caudate  nucleus,  loi,  105,  109,  115, 

116.  123,   125,   137,   145, 

204,  207,  209,  235 
Cava  subarachnoidealia,  8 
Cavernous  sinus,  3,  5 
Cavum  septi  pellucidi,  iii,  415 
Cell-body  of  neurone,  167,  169 
Cell-columns  of  cord,  340,  341,  344, 

345, 347 

Cells  of  anterior  columna,  340 

of  granular  laver  of  cerebellum, 

258 
of  posterior  columna,  347 
of  Purkinje,  257,  258,  259 
Cell  and  fiber  lamination  of  cerebral 
cortex,  183,  185,  189,  193, 
197 


Ccllulifugal  conduction,  168 
Cellulipetal  conduction,  168 
Ccntermedian(Luysi)oflhalumus,2i  1 

of  abstract  concept,  182,  182 

of  concrete  concept,  182,  183 

of  crescent,  344 

of  equilibrium,  71,  181 

of  intonation,  71,  181 

of  macular  vision,  67 

of  muscular  sense,  178 

of  optic  reflexes,  324 

of  orientation,  71,  181 

of  smell,  82,  94,  181 

of  stereognosis,  1 78 

of  taste,  94,  98,  181 

of  visual  memories,  67,  69 
Central  canal  of  cord,  399,  428 
of  lower  medulla,  305 

cells   of  anterior  columna,  343, 

345 

gray  substance  of  medulla,  305 

lobule,  247,  250 

part  of  lateral  ventricle,  112 

sulcus  (Rolandi),  56,  57,410,414 

sulcus  of  island,  72 

tegmental  tract,  277 

or  veutricular  gray  matter,  221 
Centrifugal  arteries,  331 

fibers  of  corpus  striatiun,  207 
Centripetal  arteries,  331 

iibers  of  corpus  striatum,  208 
Centrosome,  167 
Centrum  semiovale,  177 
Cerebellar  hemispheres,  242 

notches,  244 

vermis  or  worm,  243 
Cerebello-olivary    fibers,     265,     292, 

295,  312 

Cerebello-spinal     fasciculus     (poste- 
rior), 288,  301 
Cerebellum,  31,  33,  35,  36,  37,  38. 
43,  53,  209,  242,  418,  419 

blood  supply  of,  27,  29,  30 

veins  of  29,  30 
Cerebral  aqueduct  (Sylvii),  4,  30,  34 
87,  132,  147,  152,  247,  417 

cortex  and  medulla,  177,  411 

gray  substance,  174 

hemispheres,  30,  35,  37,  51,  98 

localization,  177 

ner\-es,  47,  318 

peduncle.  209,  267 

reflexes,  392 


436 


INDEX. 


Cerebro-pontal   paths,    frontal,   tem- 
poral and  intermediate,  369 
Cerebro-spinal  paths,  366 

reflexes.  393 
Cerebrum,  30,  31,  33,  50 
Cervical  enlargement  of  spinal  cord, 

333'  334,  335 
flexures,  402 
Charcot's  artery  of  cerebral  hemor- 
rhage, 18 
Chiasma  opticum,  38,  82,  83 
Chief    nucleus    of    vestibular    nerve 

(Schwalbe),  283 
Chorioid  epithelial  lamina  of  lateral 
ventricle,  124,  412 
plexus   of  fourth  ventricle,   13, 
290,  314,  424 
of  lateral  ventricle,  10,  80,  90, 
120,    124,    125,    127,    136, 
145,  209,  235,  289,  406, 
412,  416 
of  third  ventricle,  10,  129, 132, 
209,  417 
tela  of  fourth  ventricle,  10 
of  third  ventricle,   10,  11,  90, 

95,  131.  132.  135 
Chorioidal  fissure,  80,  86, 90, 95, 10 1, 
124,    127,    133,   406,   407, 
409,   411 
groove   of   thalamus,   137,  140, 

147 

vein.  II,  21,  129 
Chromophilous  cells,  204 
Ciaglinski's  sensory  tract,  350 
Cilio-spinal  centers,  298 
Cingulum,  237,  238 
Circular  sinus,  4,  5 

sulcus,  70 
Circulation  of  cerebrum,  14 

of  rhombencephalon,  14,  24 
Circulus  arteriosis  (Willisi),  14 
Cistema  cerebello-meduUaris,  9 

interpeduncularis,  9 

pontis,  9 
Claustrum,  loi,  145,  204,  209,  235 
Clava,  13,  246,  289,  300,  310 
Cochlear  nerve,  280 

nucleus,  280,  302,  305,  309,  323 

path,  386 
Cohnheim's  end  arteries,  18 
Collaterals,  168,  169,  398 
Collateral  fissure,  75,  80,  81,  86,  90, 
91,  95,  loi,  410 


Colliculi    of    corpora   quadrigemina, 
147,  149,  163,  243,  246 
CoUiculus   facialis,    149,   269,   270, 
277,  317 
inferior  of  corjjora  quadrigemina, 

149,  163,  220 
superior  of  corpora  quadrigem- 
ina,   149,    159,    163,    219, 
243,  416 
Columna  anterior,  339 

fomicis,  105,  I  TO,  131,  239 
lateralis,  335,  34 1,  344 
posterior,  347 
Columns  of  fornix,  no,  131, 132,  137, 

139,  209,  212,  235 
Comma  tract  of  Schultze,  341/361 
Commissura  anterior  alba,  351I5 
anterior  cerebri,  31,  136,  201 
anteria  grisea,  350 
grisea  of  spinal  cord,  338,  350 
habenularum,  in,  135 
hippocampi    (Fornix),    51,    no, 

125,   I3I'   236,   412,   414 
inferior  (Guddeni),  218,  221 
posterior  cerebri,  132 
posterior  of  cord,  350 
superior  (Meynerti),  218,  221 
Commissural    fibers   of    cerebellum, 
262,  265 
of  cerebrum,  224,  234 
nucleus,  305,  306 
Common  sensory  area  of  cerebrum,  178 
nuclei  of  cerebral  nei-ves,  322 
paths  375,  ?77,  379 
Confluens  sinuum,  2 
Conus  meduUaris,  31,  334 
Co-ordinating  and  equilab rating  re- 
flex, 390 
Convex  surface  of  fore-brain,  52 
Corona  radiata,  209 
Cornu  anterius  ventriculi  lateralis,  120 
commissural  tract,  345,  362 
inferius  ventriculi  lateralis,  123, 

133 

posterius  ventriculi  lateralis,  123, 

133 

Corpora  albicantia  (see  corpus  mam- 
milla), 85,  221 

geniculata,  30 

quadrigemina,  28,  30,  37,  109, 
146,  163,  219,  418 

mamillaria  (see  corpus  mam- 
miUare) 


INDEX. 


437 


Corpus  callosum,  6,  25,  30,  51,  87, 
91,  loi,  104, 109,  117, 112, 
145,  209,  234,  235,  411, 
413,  414 

dentatum,  260 

geniculalum  mediale,  143,  147, 
149,  218,  221 

geniculalum  laterale,  143,  147, 
218,  416 

Luysi,  143,  145 

mammilare  (or  corpora  mam- 
millaria),  ^o,  38.  47,  75,  82, 
S5.  87,  95,  131,  145,  153, 
207,  209,  221,  267,  417 

medullare  cerebelli,  242,  244, 247, 
255,    261,    262 

pineale,  30,  75,  132,  137,  243 

restiforme,  149,  246,  264,  288, 
301,  421 

striatum,  28,  36,  37,  98,  115, 
204,  410 

trapezoideum,  272 
Cortex  of  cerebellum,  242,  256,  258, 

259  , 

and  ganglia  of  cerebellum,  421 
Cortical  areas  of  convex  surface  of 
cerebrum,  175,  182 
of  medial  surface  of  cerebrum, 

179,  183 
of  smell,  82,  94,  181 
gray  matter  of  cerebrum,  177 
connection  of  abducent  nucleus, 
282 
of  anterior  columna,  343 
of  cochlear  nuclei,  310 
of  facial  nucleus,  282 
of  genetic   nuclei   of   cerebral 

nerves,  324 
of  motor  nuclei  in  medulla, 305 
of  nucleus  alae  cinereas,  306 
of  oculomotor   and    trochlear 

nuclei,  223 
of  olfactory  nucleus,  324 
of    terminal    nuclei    of    optic 

nen-e,  324 
of  trigeminal  nucleus,  281,  307 
of  vestibular  nuclei,  308,  323 
fillet,  104,  160,  216,  232,  233 
localization,  177 
system  of  arteries,  15 
Corticifugal  fibers  of  cerebrum,  225 
Corticipetal  projection  fibers,  231 
Cortico-striate  radiation,  207 


Crista  gain,  4 

Crossed    descending    tract    of    red 
nucleus     (see     rubro-spinal 
tract) 
ponto-spinal  tract,  280 
pyramidal  tract,  287 
Crown  of  hippocampal  g>'rus,  196 
Crus  fomicis,  95,  loi.,  105,  no,  124, 

131,  133,  237 

Culmen    monticuli,    87,    243,    245, 

247,  250 
Cuneate  gyrus  (see  cuneus) 
tubercle,  13,  289,  310 
Cuneus,  25,  97 

Declive  monticuli,  87,  243,  247,  251 
Decussatio  lemniscorum,  291,  292 

pyramidum,  41,  291 
Decussation  of  brachia   conjunctiva, 
156,  161,  245,  261,    263, 

275 

of  pyramids,  209,  267,  291,  294 
Deep  transverse  fibers  of  pars  basi- 
laris  pontis,  271,  275 

veins  of  pons,  27 

vena  cerebri  media,  23 
Defecation  reflex,  391 
Degeneration  of  neurones,  171 

of  Nissl,  171 

of  Waller,  171 
Deiter's  cells,  340,  348 

dorso-lateral  vestibular  nucleus, 
280,  308 
Dendraxone,  168 
Dendraxones  of  Golgi,  191 
Dendrites,  165,  167,  169,  399,  401 
Dentate  fascia,  82,  loi,  124, 127,  415 

g>Tus,  411,  414 

nucleus,  255,  260,  277 
Derivatives   and  ventricles   of  brain 
vesicles,  403 

of  dicnccphalon,  415 

of  mesencephalon,  417 

of  metencephalon,  419 

of  myelencephalon,  424 

of  telencephalon,  404 
Descending  anterior  ccrebello-spinal 
tract,   287,  298,  305,  311, 
341,  345,  352;  356 

part  of  medial  longitudinal  bun- 
dle, 158 

postero-medial  tract,  361 

postero-lateral  tract,  362 


438 


INDEX. 


Descending  root  of  trigeminal  nerve, 
163,  275,  277 
tracts  of  spinal  cord,  352 
Destruction    of  special  sense  paths, 

389 
Destructive  lesions  of  cerebral  cortex, 

183 
Development  of  brain,  401 
of  neurones,  172 
of   peripheral    common    sensory 
neurones,  400 
Diameters  of  spinal  cord,  333,  334, 

335 
Diagram  of  brain  ventricles,  141 
Diaphragma  sellae,5,  84 
Diencephalon,  28,  30,  127,  402,  415, 
Digitations  of  hippocampus,  124 
Direct  cerebellar  tract  (see  posterior 

cerebello-spinal  tract),  264, 

30T'  357 
motor  paths,  367 
pyramidal  tract  (see  anterior  py- 
ramidal tract) 
Dorsal     accessory    olivary    nucleus, 
297,  312 
longitudinal  fibers  of  pons,  272 
tegmental    decussation    (Mey- 

nerti),  156,  157,  159 
view  of  brain  ventricles,  141 
zone,  422,  427 
Dorso-medial  cells  of  CK)rd,  340,  341 
vestibular  nucleus  (of  Schwalbe), 
280,  307 
Dorso-lateral   cell-group,    341,  343, 

345 

vestibular  nucleus  (Deitersi),  280, 
308 
Dorso-ventral  fibers  of  medulla,  292 

of  spinal  cord,  351 
Dura  mater  encephali,  i 
of  brain,  i,  6 
of  cord,  326,  327,  329 
spinalis,  326 
of  brain  and  cord  compared,  7 

Ectorhinal  sulcus,  80,  86,  90,  95 
Efferent  neurone,  169,  171 

paths,  366 

root,  363 

sympathetic  fibers,  344 
Elements  of  olfactory  bulb,  196,  203 
Embryologic  divisions  of  the  brain- 
table,  30 


Embryological    method   of    locating 

tracts,  352 
Embryology  of  brain  and  spinal  cord, 

395 
Embryonic  neurones  of  spinal  cord, 

Eminentia  cinerea,  317 

coUateralis,  93,  124,  131,  133, 
411 

medialis,  290,  423 
Emissive   motor   area   of  cerebrum, 

63.  177 
Encephalon,  31 

general  considerations,  34 
End  arteries  of  Cohnheim,  18 
End-brain,  30,  33,  50,  51,  73 
End-brush  of  axones,  168 
Entry  zone,  341,  345,  359 
Ependymal  cells,  173,  174,  397 

layer  of  embryo,  398,  425,  429 
Epiblast,  395,  396 
Epiblastic  sustentacular  tissue,  173 
Epiphysis,  135 
Epithalamus,  28 
Equilibrium  reflex,  393 
Experimental    methods    of    locating 

tracts,  353 
Exterior  surface  of  fore-brain,  51 
External  arcuate  fibers,  265,  292 

capsule,    loi,  105,   113,   145, 
209,  235 

layer  of  large  pyramids  of  cere- 
brum, 184,  187 

perpendicular  sulcus,  67,  69 

spinal  veins,  331,  332 

surface  of  temporal  lobe,  70 

veins  of  cerebrum,  22 

Facial  nerve,  45,   153,  209,  321 
Facies  anterior  of  medulla,  286 
cerebelli  inferior,  251 

superior,  248 
convexa  cerebri,  52 
lateralis  of  medulla,  287 
posterior  of  medulla,  288 
Falx  cerebelli,  2,  3 

cerebri,  i,  2,  3,  4,  6,  407 
Fascia  dentata,  90,  97,  131,  200,  201    . 
Fasciculus    antero-laleralis    proprius, 
297,  305,  311,  341/345. 
354 
ascendens  cerebello-spinalis  an- 
terior, 298,  356 


INDEX. 


439 


Fasciculus    cercbello-spinalis    poste- 
rior, 301,  357 
cerebro-spinalis  anterior,  355 

lateralis,  358 
cuneatus,  335,  341,  361,  427 
descendcns  cerebello-spinalis  an- 
terior, 298,  356 
gracilis,  335,  .341,  360,  427 
lateralis  proprius,  298 
longitudinalis  inferior,  131,  201, 
237,  240 
inedialis,  156,  276,  296,  354 
pyramidalis,  148 
superior,  237,  240 
ventralis   (see  anterior  longit- 
udinal bundle) 
mammillaris  princeps,  no,  222 
marginalis  (Lissaueri),  341,345, 

359 
occipito-frontaUs   (Foreli),    23Q, 

241 
olivaris,  208,  277 
pedunculo-mammillaris,  85,  no, 

222 
perpendicularis,  237,  241 
posterior  proprius,  362 
thalamo-mammillaris     (Vicq    d' 

Azyri),  85,  no,  237 
uncinatus,  237,  239,  240 
Fasciola  cinerea,  82,  97,  414 
Fastiguum,  244,  247 
Felt-work  of  Kaes,  184,  191 
Fiber  zones,  184 

Fibers  of  granular  layer  of  cerebel- 
lar cortex,  260 
of  Meynert,  192 

of    superficial    layer  of   cerebral 
cortex,  257 
Fibrillie  of  neurones,  167 
Fibrous  sheath  of  Henle,  168 
Fifth  nerve,  3 

ventricle,  in,  121,  415 
Fila  lateralia  pontis,  271 
Fillet,  159 

decussation,  292,  305,  425 
Filum  terminale  externum,  330 

terminale  internum,  330,  ;};^;^,  334, 

334 

Fimbria  hippocampi,  124 
First  cerebral  vesicle,  35 
Fissura  calcarina,  25,  86,  89 

cerebri  lateralis,  53,  55,  57,  61, 
63,   91 


Fissura   chorioidea,  80,   86,  90,  95, 

411 
collateralis,  75,80,81,86,90, 131 
hippocampi,  80,  86,  90,95,  131, 

201 
longitudinalis    cerebri    35,     39, 

.43,  S2>   53 
mediana  anterior,  337 

posterior,  337 
occipito-parietalis,  409 
rhinahs,  93 

transversa  cerebelli,  36 
cerebri,  35,  55 
Fissural  arteries,  331 
Fissure,  52 

Fissures  of  convex  surface  of  cere- 
brum, 52 
of  medial  and  tentorial  surface, 

85 
of  spmal  cord,  335,  337,  430 
Flechsig's  oval  tract,  361 

sensory  bundles  of  internal  cap 

sule,  232 
superior  nucleus,  308 
Flexures,  403 
Flocculus,  i.  of  cerebellum,  209,  245, 

252,   253,   420 
Floor  of  fourth  ventricle,  246,  270, 

290,  314,  334 
Floor-plate  of  neural  tube,  400,  422, 

427 
Folium  vermis,  87,  243,  247,  251 
Foramen  cjecum  (Vicq  d'Azyri),  153 
inter^'entriculare  (foramina  inter- 
ventricularia)  (^fonroi),  30, 
87,  n2,  132,  141,411 
Forceps  major  of  corpus   callosimi, 

108,  123 

minor  of  corpus  callosum,   108, 
120 
Foreli's  ventral  tegmental  decussation, 

156,  157,  I5Q 
Fore -brain,  30,  31,  35,  50.  51.  407 
Formatio  reticularis  of  cord,  335 

of  mid-brain,  155,    157,  159, 

161,  273,  339 
of  pons,  273.  275,  277 
FomLx,  II,  30,  87,  91,95,97,  loi. 

109,  121,    129,  131.  145, 
237,  238,   412,  413 

Fossa  cerebri  lateralis,  413 

interpeduncularis,  146,  153,  159 
rhomboidea,  314 


440 


INDEX. 


Fourth  nerve,  3,  5,  13,  289 

ventricle,  9,  13,  ^S'  37,  I47, 
242,  275,  285,  289,  313, 
422 

Fovea  inferior,  149,  290,  317 
superior,  149,  269,  317 

Foveolas  granulares,  6 

Fraenuluin  veli,  13,  147,  246 

Frenulum  of  Giacomin,  94 

Frontal  lobe  of  cerebrum,  37,  53,  59, 

73.  75,  87,  91,  98 
part  of  internal  capsule,  103 
pole  of  cerebrum,  50,  53 
stalk  of  thalamus,  103,  216,  226, 

232_ 

Fron to-marginal  sulcus,  60 
Fronto-pontal  tract,  103,   151,    159, 

225,  226 
Function  of  cerebellum,  242 

of  neurones,  171 

of  posterior  root,  364,  365 
Functional  areas  of  cerebrum,   I75, 

177,  179,  182,  183 
Funiculus  anterior,  335,  352 

cuneatus,  288,  300,  305,  311 

gracilis,  288,  300,  305,  311 

lateralis,  335,  352 
of  medulla,  153,  287 

posterior,  335,  352 

separans,  270 
Fusiform  gyrus,  79,  81,  95 

layer,  191 

Galen's  great  cerebral  vein,  136 

internal  cerebral  veins,  129 
Gambault     and    Philippe's    median 

triangular  tract,  361 
Ganglia,  400,  401 

of  cerebral  nerves,  400 
Ganglion  interpedunculare,    151 

jugulare,  49 

nodosum,  49 

semilunare  (Gasseri),  45,  267 

spinale,  364 
Ganglionar  gray  matter  of  cerebellum, 
260 

of  cerebrum,  204 
Ganglionic     cells     (Bevin     Lewis), 
191 

system  of  arteries,  18 
Gelatinous  substance  (Rolandi),  339, 

341 

Genetic  nucleus,  i.,  42,  319,  363 


Genetic  nuclei   of  anterior  roots   of 
spinal  nerves,  349,  363 
of  cerebral  nerves,  319,  324 
nucleus    oculomotor    nerve,    45, 
152,  223 
trochlear  ner\^e,  45,  152,  223 
Geniculate  bodies  (metathalamus) ,  5  t  , 

204,  207,  417 
Gennari's  or  Baillargic  line,  188 
Genu  capsulas  interna;,  103,  113 
inferius  of  central  sulcus,  56 
internum  of  facial  nerve,  283 
superius  of  central  sulcus,  56 
of  corpus  callosum,  11,  95,  108, 
109,  120,  121 
Germinal  area,  35 

cells  of  neural  crest,  172 
of  His  in  neural  tube,  172 
Giant  pyramids  (Betz),  188 
Globus  pallidus  of  lentifonn  nucleus, 

116,  145,  209,  235 
Glomus  chorioideum,    11,  120,  125, 

129 
Glossopharyngeal  nen^e,  5,  46,  153, 

209,  293,  320,  321 
Golgi  cells,  165 

of  spinal  cord,  165,  340,  347 
dendraxones,  191 
Goll's  column,  300,  360 
Gordinier's  writing  center,  175,  178, 

182 
Gowers's  tract,  276,  356 
Granulationes  arachnoideales,  5 
Granular  layer  of  cerebellar  cortex 

258 
Granule  cells  of  cerebellum,  258,  259 
Gray  anterior  commissure,  335,  35° 
commissure  of  cord,  335,  338. 

35° 
crescent  of  spinal  cord,  339 
matter  of  cerebellum,  256 
of  cerebrum,  164 
of  medulla,  302 
of  pons,  278 
of  spinal  cord,  338 
of  stratum  nucleare,  278,  302 
Gratiolet's     radiatio     occipito-thala- 

mica,  217 
Great  anastomotic  vein  (of  Trolard), 

23 
cerebral  vein  (Galeni),  3,  10,  21, 

136 
middle  meningeal  artery,  6,  7 


INDEX, 


441 


Guddcn's    inferior  commissure,  218, 

221,    235 

Gustatory  center,  179,  181,  183 

paths,  389 

radiations,  232 
Gyri  breves  insuLne,  65,  72 

insuhe,  65,  72,  235 

occipitales  laterales,  68 
■  superiores.  68 

temporales  transversi,  70 

transitivi,  64 

of  convex  surface  of  cerebrum, 

59 
of  medial  and  tentorial  surface,  93 
Gyrus  angularis,  61,  63,  67 

centralis  anterior,  59,  6q,  61 

posterior,  61,  63,  64 
cinguli,  93,  95,  97,  203 

cortex,  of  203 
circumambiens,  82,  94 
cunei,  89 

cuneo-lingualis,  90 
fomicatus,  93,  95,  97 
frontalis  inferior,  59,  61 

medius,  59.  61 

superior,  59,  61,  95,  97 
fusiformis,  75,  81,  97 
hippocampi,   79,  81,  93,  94,  95, 

97 
lingualis.  8t,  95,  97 
longus  (furcalis)  insulte,  65,  72 
marginalis,  97 
orbitalis  anterior,  74,  75 

lateralis,  74 

medialis  74,  75 

posterior,  74,  75 
profundus  transitivus,  64 
rectus,  74,  75,  95,  97 
semilunaris,  82,  94 
subcallosus,  75,  87,  91,  97,  107, 

200,  414 
supracallosus,  107,  414 
supramarginalis,  61,  63,  67 
temporalis  inferior,   61,   70,    71, 

75 

medius,  61,  70,  71 
superior,  61,  70,  71 
transversus  insube  (of  Eberstal- 
ler),  72 

H-shaped  column,  339 
Helwig's  triangular  tract,  298,  305, 
312,  357 


Hemisphere  vesicle,  405,  409 

of  cerebellum,  41,  242,  245,  252, 

419 
of  cerebrum,   35,    39,   43,    47, 

53,  405 
Hcmispheria  cerebelli,  242,  245,  252 
Hiatus  (Sylvii),  99,  115 
Hind-brain,  31,  33 
Hippocampal  fissure,  80,  86,  90,  91, 
95,    loi,    201,   409,   411, 
416 
g>Tus,  81,  94,  95 
region,  201 
Hippocampus,    80,    90,    10 1,    113, 
124,   131,   133,   145,  409. 
414,  416 
minor  (see  calcar  avis),  125,  133 
His  (germinal  cell  in  neural  tube),  172 
Histologic  layers  of  neural  tube,  427 

of  spinal  cord,  397 
Hoche's  bandalctte.  362,  345 
Horizontal  anterior  ramus  of  lateral 
fissure  57, 
part  of  interparietal  sulcus,  57 
sulcus  of  cerebellum,  243,  245, 
247,  420 
Hypoblast,  396 

Hypoglossal  nerve,  5,  49,  153,  293, 
322 
nucleus,  295,  303 
triangle,  317 
Hypophyseal  region,  37 
Hypophysis  cerebri,  37,  38,  47,  82. 

84,  267 
Hypothalamic  nucleus,  143,  145 
Hypothalamus,  82,  143,  221 

Impressio  pctrosa,  53 
Incissura  pra;occi{)italis,  61, 

temporalis,  80 

tentorii,  2 
Indifferent  cells,  397 
Indirect  motor  paths,  371 
Inferior  cerebral  veins,  13,  2-^ 

colliculi  of  corpora  quadrigem- 
ina,  147,  149,  16^,  220. 
418 

commissure  (Guddeni),  218,  221, 

efterent  veins  of  pons,  27 
external  cerebellar  veins,  29 

frontal  arter\',  19,  22 
fovea,  270,  290,  317 


442 


INDEX. 


Inferior  frontal  gyrus,  39,  59,  60,  61 
sulcus,  39,  57,  59 
gray  commissure   of  fore-brain, 

84 
horn   of   lateral  ventricle,   10 1, 
105,   123,   133,   141,  145 
internal  frontal  artery,  19 
lamina  of  internal  capsule,   99, 

113,  115,  123 
lateral  occipital  gyrus,  61 
longitudinal  fasciculus,  137,237, 

240 
medullary  velum,  13,  244,  245, 

247,  262 
olivary  nucleus,  209,  297,  305, 

312,  425 
parietal  lobule,  61,  63,  64 
pedimcles  of  cerebellum,  246,  264 

of  thalamus,  100,  145 
petrosal  sinus,  3,  3,  4,  5 
postcentral  sulcus,  57,  63 
precentral    sulcus,  39,  57,   59, 

414 
quadrigeminal     colliculus,     13, 
147,   149,  163,   204,   207, 
220,  418 
sagittal  sinus,  2,  3 
semilunar  lobule,  252,  255,  255, 

420 
surface  of  cerebellum,  251,  252 

of  island,  74         ^ 
striate  veins,  23 
temporal  g}'rus,  61,  70,  71,  79 
sulcus,  70,  80,  81,  86,  93 
Infero-lateral  border,  52 
Infundibulum,  4,  9,  47,  75,  82,  84, 

109,  131 
Insula  (Reili),  71,  74,  75,  105,  125, 

207,  209,  267,  410 
Inter-brain,  30,  S3'  37,  5°'  SL  73- 

127,  415 
Interior  surface  of  fore -brain,  98 
Interlobar  boundaries,  55 
Intel-mediate  nerve,  45,  153,  320 
olfactory  stria,  77,  78 
tract  ICO,  148,  159,  225,  226 
Inteimedio -lateral    column    of    cell- 
bodies,  341,  344 
Internal  capsule,  99,  loi,  105, 109, 
113,  115,  145,  209,226, 
412,  417 
carotid  artery,  3,  4,  5, 14-  15, 1 9 
cerebellar  veins,  29 


Internal  layer  large  pyramids  of  cere- 
bral cort«x,  184,  188 
medullary  lamina  of  thalamus, 

208 
orbital  artery,  16 
spinal  veins,  331,  332 
veins  of  cerebrum,  21 
Interparietal  sulcus,  39,  43,  57,  63, 

414 
Interpeduncular  fossa,  145,  146,  153, 
159,  161,  209 
ganglion,  151 
space,  38 
Interventricular  foramen  (of  Monro), 
36,  37,  95,  112,  128,  235, 

405 
Intumescentia  cervicalis,    2;^^,   334, 

335 

lumbahs,  334,  335 
Inverted  pyramids  of  Martinotti,  191 
Island  (of  Reil),  71,  74,  75,  98,  105, 

414 
Isthmus  gyri  fomicati,  94 

rhombencephali,  28,  ;^7„  418,  419 

Jugular  ganglion,  49 

Kaes,  meduUation  late  in  life,  412 
Key  and  Retzii,    apertura    lateralis 
ventriculi  quarti,  9,  290 

Lamina  afi&xa,  119 

chorioidea  epithehahs,  115,  119, 

124 
cinerea  terminalis,  30,  36,  38,  82, 

83.   87,  91,  95'    I09'   131. 

139,  221,  413 
quadrigemina,  30,  163 
rostrahs  of  corpus  callosum,  108 
Lamina;  meduUares,  262 
Lateral  apertures   (Key  and  Retzii), 

9,  10,  290 
area  of  medulla,  293,  298 
cerebral  fossa,  410,  413 
cochlear  nucleus,  309 
column  of  cell -bodies,  340,  341, 

345 

column  of  medulla,  2S7 
columna  of  cord,  335,  344 
fasciculus    proprius,    287,    298, 

354 
fillet,   13,  159,   160,   161,  246, 

274.  275,  309 


INDEX. 


443 


Lateral  fissure  of  cerebrum  (Sylvii), 

53,55-57,61,63,91,414 

geniculate  body,   140,  143,  157, 

204,  207,  218 
longitudinal    stria    (see    longitu- 
dinal stria) 
nucleus  of  thalamus,  211 
occipital  g}Ti,  43,  68,  69 

sulci,  57,  68 
olfactory  siria,  75,  78,  207 
orbital  arteries,  16 

gyrus,  74 
ponto-spinal  tract  (CoUieri),  355, 

373 
pyramidal  tract,  287,  294,  341, 

345, 358 
recess  of  fourth  ventricle,  289 
sulcus  of  mid-brain,  159,  243 
surface  of  medulla,  2S7 
ventricles,  30,  34,   36,  37,  in, 

112,    145,   405,   412 
view  of  brain  ventricles,  141 
Layers  of  cells  of  cerebral  cortex,  184 
Laver  of  fusiform  cells  of  cerebral  cor- 
tex, 184 
of  large  pyramids,  external,  184, 

187 
of  large  pyramids,  internal,  184, 

188 
of   medium    sized    pyramids    of 

cerebral  cortex,  184,  187 
of   small    pyramids    of    cerebral 

cortex,  184,  187 
of  stellate  and  polymorphous  cells 
uf  cerebral,  cortex,  184,  188 
Law  of  Waller,  353 
Lemniscus,  159 

lateralis,  160,  274 
medialis,  160,  273,  295 
superior,  274 
Lenticulo-striate  artery,  18 
Lentiform  nucleus,   loi,  105,  113, 

116,  145,  204,  226,  235 
Lesions  of  anterior  columna,  344 
of  corpus  striatum.,  208 
of  gray  substance  in  cord,  350 
of  special  sense  paths.  380 
in  medulla,  313 
in  posterior  columns,  362 
Ligamentum    dcnticulatura,    3,   327, 

329,  33° 
Limbic  lobe,  73,  Si.  87,  91,  93,  97,  98 
Limen  insulse,  72,  77,  79 


Line  of  Raillarger,  184,  188,  213 
Linea  splendens,  327,  329 
Lingual  gyrus,  95,  97 
TJngula  cercbelli,  13,  87,  247,  250 
Lissauer's  fasciculus  marginalis,  341, 

345, 359 
Lobes  of  convex  surface  of  cerebrum, 

59 
of  lower  surface  of  cerebellum, 

253 
of  medial  and  tentorial  surface  of 

cerebrum,  93 
of  superior  surface  of  cerebellum, 
250 
Lobules  of   cerebellar  vermis,  247, 

249.  253 
Lobulus  biventer,  245,  254 
centralis,  87,  245,  250 
gracilis,  245,  256 
paracentralis,  64,  97 
parietalis  inferior,  63,  64 
superior,  63,  64 
Lobus  centralis  cerebeUi,  250 
culminis  cerebelli,  243,  250 
declivis  cerebelli,  243,  250 
folii  verm.is,  243,  251 
frontalis,  59 
limbus,  81 

linguliB  cerebelli,  250 
ncduli,  253 
occipitalis,  67 
parietalis,  63 
pyraformis,  97 
pyramidis,  254 
temporalis,  69 
tuberis,  255 
uvulae,  254 
Localization  of  cerebral  function,  177 
Locus  ca?ruleus,  269,  270,  317 
Long  association  fibers  of  cerebrum, 

23S 
Longitudinal  fibers  of  medulla,  293 
of  lateral  area  of  medulla,  298 
of  pons,  272,  275 
of  posterior  area  of  medulla. 

300 
of  spinal  cord,  352 
fissure  of  cerebrum,  35,  39,  43, 

52,  53,  209,  235 
strice,  medial  and  lateral,  97,  107, 
117 
Lower  segment  paralysis,    344 
surface  of  cerebellum,  253 


444 


INDEX. 


Lumbar  enlargement  of  spinal  cord, 

334.  335 
Liiys,  center  median  of  thalamus,  211 
nucleus  hypothalami cus  of,  143, 
151,  218 
Lymph  spaces  of  cerebellum,  30 
of  cerebrum,  23 
of  medulla,  24 
of  spinal  cord,  332 

Magendi,  apertura  mediana  ventric- 

uli  quarti,  290 
Mammillary  bodies,  38,  51,  75,  85 
Mantle  layer,  398,  425,  428 
Marginal  gyrus,  95,  97 

sinus,  5 

tract,     Lissauer's,     341,     345, 

359 
velum..  397,  397,  398,  425,  428 
Margo-infero -lateralis,  52,  75 
Margo  occipitahs  lateralis,  52,  .75 
medialis,  52,  75 
orbitalis  medialis,  52,  75 
superciliaris,  39,  52,  75 
supero-medialis,  39,  52 
Martinotti's  inverted  pyramids,  191 
Massa intermedia,  95,  137, 139, 145, 

221,  222,  417 
Medial    accessory  .  olivary    nucleus, 

295.    297,   305,   3Tf2 

cerebral  veins,  22, 
column  of  cell-bodies,  340 
fillet,  157,  159,  160,  161,  231, 
273-   275,  277,  292,  295, 

29S'  297,  305 
geniculate  body,  140,  143,   146, 

147,  149,'  157,  159,  204, 

207,  218 
longitudinal  bundle,    156,    157, 

159,   161,  275,   276,   277, 

295,  296,  297,  305,  311, 

341,  345,  354 

stria  (see  longitudinal  stria), 
nucleus  of  thalamus,  208 
occipital  border,  52,  75 
olfactory  stria,  75,  77,  78 
orbital  border,  52,  75 

gyrus,  74,  75 
ponto-spinal  tract,  CoUieri,  158, 

297.  355.  373  . 
surface  of  fore-brain,  92,  95 
and  lateral  olfactory  stri*,  47, 

75,  77.  78 


Median  aperture  (Magendi),  9,  9, 10, 
13,  289,  290 

triangula,r    tract    (of    Gambault 
and  Phillipe),  361 
Medulla  oblongata,  24,  31,  33,  35,  36, 
37,  38,  87,  242,  284,  422 

spinalis,  31,  333,  334,  335 
Medullary  body  of  cerebellum,  242, 
244 

groove,  396 

laminae,  262 

plate,  395 

ridges,  395 

striae,  149,  270,  290,  309 
MeduUation,  168,  169,  429 
Membranes,  of  brain,  i 

of  spuial  cord,  326,  327,  329 
Meninges  encephali,  i 

spinalis,  326,  327,  329 

of  brain,  i 

of  spinal  cord,  426,  327 
Mesencephalic  flexure,  402 
Mesencephalon,    28,    30,    31,    144, 

402,  417 
Mesoblast,  396 

Mesoblastic  sustentacular  tissue,  174 
Metathalamus,  140,  143,  218 
Meten cephalic  flexure,  402 
Metencephalon,    28,    31,    33,    36, 

266,  402,  418 
Methods  of  locating  tracts  of  fibers, 

352 
Meynert's  association  fibers,  192,  236 
commissura   superior.  208,  218, 

221 
dorsal  tegmental  decussation,  156 

157,  159 

solitary  cells,  195 
Mid-brain,  30,  31,  33,  36,  37,  50/87, 

144,  243,  417 
Middle  association  center,  183 
brain  vesicle,  30 
cerebral  artery,  4,  15,  t6 
commissure,  137,  222 
frontal  gyrus,  39,  59,  61 

sulcus,  57,  60 
internal  frontal  arteries,  16 
meningeal  artery,  3,  5,  6,  7 
or  lateral  occipital  g}'rus,  61 
peduncles    of    cerebellum,    247, 

264 
temporal  gyrus,  61,  70,  71 
sulcus,  63,  70 


INDEX. 


445 


Midgracile  sulcus,  421 

Mixed     ascendinjj;    and     desccndin.^ 

tracts,  352 
Monro,  interventricular  foramen  of, 

95,  112,  128,  141,  405 
sulcus  hypothalamicus  of ,  Q  i ,  95, 

415 
Moss-like  appendages  of  Cajal,  259, 

260 
Motor  area  of  cerebrum,  177 
center  for  foot,  98,  178 
cerebral  nerves,  321 
fibers  of  cerebrum  225, 

of  internal  capsule,  100,  103 
memory  center  67, 
neurone,  169 
paths,  229,  366,  367,  371 
roots  of  cerebral  nerves,  321' 
root  of  spinal  nerve,  363 
speech  center,  178 
Motorial  end-plates,  168,  169 
Myelencephalon,  28,  31,  33,  266, 

284,  402,  422 
Myelin    sheath    of  axones  and  den- 
drites, t68 
Myelinization,  412,  429 

Naming  center,  71,  181 

Neopallium,  28,  98 

Nerves  of  arachnoid,  9 
of  dura  mater,  7 
of  pia  mater,  13 

Nervi  cerebrales,  318,  421,  425 
olfactorii,  42,  320 

Nervus  abducens,  45,  267,  321 
accessorius,  49,  267,  322 
acusticus,  46,  267,  320 
facialis,  45,  267,  321 
glossopharyngcus,  46,  267,  320, 

321 
hypoglossus,  49,  267,  322 
intermedins,  45,  267,  320 
oculomotorius,  42,  267,  321 
opticus,  25,  42,  83,  267,  320 
trigeminus,  45,  267,  320,  321 
trochlearis,  45,  267,  321 
vagus,  46,  267,  321 

Neural  canal,  396 

crest,  35,  172,  395,  400 
groove,  35,  395 
tube,  35,  172,  395 

Neuraxones,  168 

Neuroblasts,  39S 


Neuroglia,  172,  399 

cells,  173 

zone,  184 

of  cerebellum,  260 
Neurolemma  (Schwann),  168,  169 
Neurone  165,  167,  169,  171,  398 

center,  167 
Neurones  of  head  of  posterior   col- 

umna,  347 
Neuropore,  405 
Nuclei  of  cerebellum,  260,  261 

of  cerebral  nerve,  278,  281,  303 

of  reticular  formation,  156,  278, 

279-  304 
of  thalamus,  208 
Nucleolus  of  neurone,  169 
Nucleus  ake  cinereie,  297,  303,  304, 
305,  306,  315 
ambiguus,  297,  303,  304,  315 
amygdala?,    113,   119,  199,  207, 

239 

arcuatus,  303 
caudatus,  116 
centralis  inferior,  278,  279 

medius,  278,  279 

suj)erior,  278,  279 
commissuralis,  305,  306 
corporis  trapezoidei,  279 
dentatus,  255,  260,  261,  277 
dorsalis    (Stillingi    and    Clarki), 

348 
dorso-lateralis  (of  Dieters),  2S3, 

30!^ 
. emboliformis,  260,  261,  277 
fastigii,  261,  277,  260,  262 
funiculi  cancati,  270,  305,  311, 
310 

gracilis,  270,  305,  311,  310 
globosus,  260,  261,  277 
habcnulse,  140,  211 
hypothalamicus  I.uysi,  143,  151, 

204,  218 
incertus,  270 
intercalatus,  270 
lateralis  inferior,  297,  303,  304 

medius,  278,  279 

superior,  156,  220 
lentiformis,  loi,  105,  116,  209 
n.  abducentis,  281 

cochlearis,  270,   315,  309 

facialis,  282 

oculomotorii,  45,  155,  315 

trochlearis,  45,  155,  315 


446 


INDEX. 


Nucleus  vestibularis,  270,  283,  305, 

307.  315 
olivaris  inferior,  312 
originis,  42,  319,  324,  363 
pontis,  272,  278,  421 
ruber,  217 

terminalis,  42,  319,  365 
tractus  solitarii,  302,  305,  306 
spinalis  n.  trigemini,  2Q5,  305, 

311,  314,  306 
of  anterior  tubercle,  211 
of  abducent    nerve,    277,    281, 

315 

of  accessory  nerve,  304,  315 

of  Bechterew,  277,  308 

of  coUiculus  inferior,   161,   164, 

220 
of  corpus  mainmillare,  85,  157 
of  descending  root  of  trigeminal 

nerve,  155 
of  descending  root  of  vestibular 

nerve,  280,  2S3,  308 
of  external  arcuate  fibers,  302 
of  facial  nei-\'e,  277,  282,  315 
of  fascia  dentata,  201 
of  fourth  nerve,  155,  315 
of  hypoglossal  nerve,  303,  315 
of  neurone,  167,  169 
of  oculomotor  nerve,  152,  315 
of  optic  nei"ve,  31^5 
of  pulvinar,  208 
of  third  nerve,  152,  315 
of  trapezoid  body,  272,  278,  279, 

280 
of  trigeminal   nerve,    277,    281, 

315 

of  trochlear  nerve,  152,  223,  315 
Ninth,  tenth  and  eleventh  nerves,  3 
Nissl  bodies,  167,  169 

degeneration,  171 
Nodes  of  Ranvier,  168,  169 
Nodular  ganglion,  49 
Nodule  of    cerebellum,    245,    247, 

252,  253 
Nodulus  cerebclli,  87,  253 
Notochord,  396 
Obex,  13,  270 
Oblique    fasciculus    of   pons,    267, 

269 
Occipital  lobe,  53,  67,  75,  87,  91,  98 

part  of  internal  capsule,  103 

pole,  50,  53,  68 

sinus,  2,  5 


Occipito-parietal  fissure,  409,  411 
sulcus,  17,  43,  53,  56,  57,  86, 

89.  91,  95 

Occipito-thalamic     radiation,     137, 

213,  217,  226,  234 
Ocular  reflex  arcs,  355 
Oculomotor    nerve,    42,    145,    153, 
209,  321 

sulcus,  146,  159 
Olfactory  bulb,  37,  47,  75,  77,  195, 
203,  207 

center,  97 

cortex,  195 

diverticulum,  36,  37 

islets  (Calleja),  199 

lobe,  73,  77,  98 

nerves,  42,  320 

path,  3S3 

projection  fillers,  232 

sulcus,  74 

strife,  75,  78 

tract,  47,  75,  77,  78,  267 

triangle,  75,  77,  79 
Oliva,  287 
Olivary  fasciculus,  162,  208,  277,  298 

nucleus,  inferior,  295,  297,  312, 

423,  425 
pedicle,  279 
Olive,  31,  41,  153,  287 
Operculum.  64,  70,  410 
Ophthalmic  division  of  fifth  nerve,  5 
Optic  center,  181 

chiasma,  30,  38,  47,  75,  83,  95, 

147,  153,  213,  235,415 
commissure  (see  optic  chiasma), 

131 
cup,  405 
nerve,  4,  38,  42,  83,  153,  213, 

320 
path,  213,  384 
radiation,    104,  213,  217,  226, 

232,   234 
recess,  91,  139,  235,  405 
reflex  center.  163,  324 

tract,  219,  355 
tract,  4,   38,  47,  75,  83,   145, 
147,  153,  157,  159,  209, 
235,    267 
vesicle,  35>  4°$ 
Orbital  lobe,  73 
Orders  of  neurones,  168 
Origin  of  anterior  root  of  spinal  nerve. 

2>^i 


INDEX, 


447 


Origin    of    posterior    root    of    spinal 

nerve,  364 
Oval  bundle  of  His,  427,  429 
tract  (Flechsigi),  345,  361 

Pacchionian  bodies,  5 
Paracentral  lobule,  64 
Paramedial  sulcus,  39,  57,  59,  60 
Parietal  lobe,  53,  63,  87,  91,  98 

stalk  of  thalamus,  103,  104,  226 
Parieto-temporal  artery,  17,  22 
Parolfactory  area  (of  Broca),  79,  86 
Pars  anterior  rhinencephali,  77 
basilaris  pontis,  266 
dorsalis  pontis,  266,  273 
frontalis   capsulas   intemag,    103, 

113 

mammillaris hypothalami,  28, 82, 

221,  417 
occipitahs  capsulas  intemie,  103, 

optica  hypothalami,  28,  82,  221, 

415 
posterior  rhinencephali,  77 
Pathological  method  of  locating  tracts, 

353 
Path  carrying  visceral,  muscular  and 
tactile  impulses,  381 
for   tactile   and  muscular  sense, 

375,  377. 
for  tactile,  pain  and  temperature 

impulses,  276,  379,  381 
through  red  nucleus,  370,  371 
Peduncle    of    corpus    caUosum    (see 
gyrus  subcallosus) 
of  flocculus,  245,  254 
Peduncular  fibers  of  cerebellum,  262 

of  cerebrum,  224 
Pedunculi  cerebri,  28,  30,  37,  146, 

147 

Pedun cuius  flocculi,  254 

Perikaryon,  167 

Permanent  fissures  and  sulci  of  cere- 
brum, 409,  414 

Perpendicular  fasciculus,  237,  241 

Petrosal    glossopharyngeal    ganglion, 
46 

Petro-squamosal  sinus,  5 

Physiological     method     of     locating 
tracts,  353 

Pia  mater  encephali,  9 
sy)inalis,  329 
of  brain,  9,  9 


Pia  mater  of  spinal  cord,  329,  329 

of  brain  and  cord  compared,  13 
Pineal  body,  36,  37,  51,  91,  95,  ioq. 
131,    132,    137,   147,   157, 
243,  416,  416 
recess.  132,  416 

stria,    135,    137,   239  (see  stria 
medullaris  thalami) 
Pituitar)'  body,  84  (see  hypophysis) 
Plexiform  layer  of  cerebral  cortex,  184 
Plexus  basilaris,  4 

chorioideus    ventriculi    lateralis, 

120,  201 
chorioideus  ventriculi  quarti,  290 
venosi  vertebrales  intemi,  332 
Plica  chorioidea  of  fourth  ventricle, 

419 
Pole  of  island,  71 
Polus  insulae,  71 

Pons  (varohi).   24,  28,  31,  3^,  37, 
38,87,101,145,153,242, 
266,  418,  421 
Pontal  arteries,  24 
Pontine  flexure,  402 
Ponto-spinal  tracts,  280,  373 
Postcentral  lobule,  72 

sulcus  of  cerebellum,  247,  248, 
420 
of  cerebrum,  63,  410 
Postdeclivil  sulcus,    243,  247,  249, 

420 
Post-dorso-lateral  cells,  343  (see  in- 

intermedio-lateral) 
Postgracile  sulcus,  421 
Postnodular  sulcus,    247,  252,  252. 

420 
Postparietal  g}rus,  63,  67 
Postpyramidal sulcus,  245,  247,  252, 

253,  420 
Posterior  anastomotic  vein,  23 
area  of  medulla,  293,  300 
association  center,  182 
brain  vesicle,  7,7,,  35 
calcarine  fissure,  89 
central  gyrus,  39,  61,  63,  64 
cerebellar   notch,    36,    243,   244 

252 
cerebello-spinal   fasciculus.    264, 

305,  311,  2S8,  341,  357 
cerebral  artery,  15,  17,  25 
chorioidal  artery,  15,  17.  19 
columna,   335,   339.   347,  427, 
429 


448 


INDEX. 


Posterior   commissure   of  cerebrum, 

95, 109,  131,  132,  137,  416 

of  cord,  335,  350 

communicating  artery,  4,  14,  15 

fasciculus  proprius.  362 

horn    of   lateral  ventricle,    123, 

131,  133,  137,  141 

inferior  cerebellar  artery,  15,  24, 

27,  29 
intermediate  sulcus  of  cord,  335, 

338 
internal  frontal  arteries,  16,  25 
lateral  sulcus  of  cord,  335,  337 

430 
lateral  sulcusof  medulla,  41, 149, 

153,  286,  295,  297 
longitudinal  bundle   (see  medial 

longitudinal  bundle) 
median  fissure  of  cord,  335,  337, 

349  >  430 

median  fissure  of  medulla,  285 

median  vein,  24 

orbital  gyrus,  74,  75 

parolfactory  sulcus,  86 

perforated    substance,    38,    47, 
109,  132,  146,  151 

pillar  of  fornix,   133   (see  crus 
fomicis) 

radicular  artery,  331 
vein,  331         , 

ramus  of  lateral  fissure  of  cere- 
brum, 57 

root  of  spinal  nerve,  327,  334, 

349,   3^3'   3'^M.  399,  427. 
428,  429 
slender  lobule,  252,  255 
spinal  artery,  24,  27,  331 
subarachnoid  space,  8,  329 
surface  of  medulla,  270,  288 

of  pons,  269,  270 
white  column  of  cord,  345,  399 
Postero-lateral    column    (Burdachi), 
300 
descending  tract,  345,  362 
ganglionic  arteries,  19,  21 
Postero-medial  column  (GoUi),  300 
Fostero-median    ganglionic   arteries, 

15,  18,  19 
Precentral  lobule  of  island,  72 

sulcus  of  cerebellum,  247,  248, 
420 
of  cerebrum,  59,  410,  414 
Precuneate  gyrus  (see  precuneus) 


Precuneus,  95,  97 

Predeclivil    sulcus,   243,  247,   249, 

420 
Preolivary  nucleus,  278,  279 
Prepyramidal  sulcus,  245,  247,  252, 

252,  420 
Prevertebral  ganglia,  401 
Primary  brain  vesicles,  30,  35,  395 
fissures  of  cerebrum,  409,  411, 

413 

Primitive  streak,  35 

Principle  or  chief  vestibular  nucleus 

(Schwalbe.'s),  307 
Processes  of  dura  mater,  i 
of  neurone,  167,  169 
Processus  durfe  matris,  i 
Projection  fibers  of  cerebellum,  262, 
263 
of  cerebrum,  224 
Prosencephalon,  30,  31,  51 
Protoplasmic  processes  of  neurones, 

169 
Psychic  acustic  center,  71,  181 

center  of   abstract  concept,  60, 

182,  183 
center  of  concrete  concept,  182, 

183 
motor  area,  1 78 
optic  center,  181 
sensory  area,  178,  67 
Pulvinarof  thalamus,  140,  149,  207, 

211,  315 
Pupillary  constriction,  394 
dilation,  394 
reflexes,  394 
Pupillo -dilator  tract,  220,  298,  355 
Purkinje's    cells,    257,    258,    259, 

265 
Putamen   of  lentiform  nucleus,   116 

145,  209,  235 
Pyramid  of   cerebellum,  247,  252, 

254 
of  medulla,  41,  153,  209,  267, 
295,  297,  311,  293,  294 
Pyramidal  cells  of  cerebral    cortex, 

165 

decussation,  291,  31 1 
motor  paths,  366 
tract,  103,  148,  159,  226,  272, 
277,  294,  355,  358 
Pyramis  cerebelli,  87,  254 
medullae  oblongatse,  294 
vermis,  254 


INDEX. 


449 


Quadrangular  lobule   243,  250  25I: 

255,  420  _ 
Quaclrigeminal  bodies,  4,  146,  147, 
163 
coUiculus,  i.,  75,  87,  163 
lamina,  146,  147,  163 

Radiatio   occipito-thalamica    (optic), 
104,  131,  217 
corporis  callosi,  234 
temporo-thalamica  (acustic),  104, 
217 
Radiations  of  corpus  callosum,  209, 

234 

of  corpus  striatum,  207,  209 

of  Mcynert,  192 
Radiary  zone  of  cerebral  cortex,  184 
Radicular  cells,  340 

veins  of  medulla  24 
Radix  anterior  of  spinal  ner\'e,  349, 

posterior  of  spinal  nen-e,  349, 

364 
Ranvier's  nodes,  168,  169 
Receptive  auditory  center,  70,  71,  181 
olfactory  center,  82,  94,  97,  17Q, 

183 
visual  center,  81,  98,  181 
Recessus  triangularis,  128,  136,  137 
Red  nucleus,  loi,  157, 159,204,217 
Reflex  arcs,  390,  391,  392 

connections  of  abducent  nucleus, 
282 
of  cochlear  nucleus,  310,  323 
of  facial  nucleus,  282 
of  genetic  nuclei,  325 
of  motor  nuclei  in  medulla,  305 
of  nucleus  alae  cinereie,  306 
of  olfactcrj^  nucleus,  324 
of  trigeminal  nuclei,  281,  307 
of  vestibular  nuclei,  308,  323, 

389 

mechanism  of  cord,  343 

paths,  390 
Regio  tegmentalis  hypothalami,  143 
Relations  of  arachnoid,  8,  326,  327, 

329 

of  dura  mater,  i,  326,  329 
of  pia  mater,  9,  327,  329 

Respirator}^  reflex,  393 

Restiform  body,    13,  41,  246,  252, 
255/280,  288,  295,  297, 

301.  423 
29 


Rhinencephalon,  28,  77,  97,  98,  406 
Rhombencephalon,   31,  33,  38,  242, 

266,  284 
Rhomboid  lip,  285,  422,  423 
Rolandic  angle,  56 
Rolando,  central   sulcus  of,  56,  57, 

61,  410 
gelatinous  substance  of,  339,  341 

345 

Roof  epithelium  of  fourth  ventricle, 
13,  289,  314 
of  third  ventricle,  132 
of   fourth    ventricle,    289,   289, 

314 

Roof-plate,  400,  416,  422.  422,  427 

Roots  of  optic  tract,  83,  147,  153 

of    spinal  nerves,  349,  362 

of  twelve  cerebral  nerves,  42 

Rostrum  of  corpus  callosum,  95,  108, 

120 
Rubro-spinal  path,  370,  371 

tract,  161,  162,  276,  295,  297, 
3oo>  305,  311,  341,  358. 
370-  371 

Salivar}'  nucleus,  283 

Schultze,  comma  tract  of,  341,  361 

Schwalbe's    dorso-medial    vestibtilar 

nucleus,  280,  307 
Schwann's  sheath,  168 
Second  cerebral  vesicle,  35 

cervical  nen^e,  3 
Secondary  brain  vesicles,  402,  403 

sulci  and  iissure,  410,  411,  414 
Sections  of  fore-brain,  407 

of  spinal  cord,  335 
Semilunar  ganglion  (Gasseri),  45 

nucleus,  278 
Sense  of  touch,  377 
Sensory  aphasia,  241 

cerebral  ner\-es,  320 

conduction  paths,  377 

paths,  229,  377 

projection  fibers,  231 

roots  of  cerebral  nerves,  320 
of  spinal  ner\-e,  349,  363,  364 

root  of  trigeminal  nerve,  307 

tract  Ciagllnski,  350 
Septo-marginal  tract,  345,  361 
Septum  pellucidum.  30.  87,  95,  07, 
III,    115,    121,    123.   209, 

235,  413-  415 
Seventh  and  eighth  ner\'es,  3 


450 


INDEX. 


Short  association  fibers  of  cerebrum, 
236.  237 

fiber  motor  paths,  373 
sensor)-  paths,  382 
Simple  reflex  arc,  391 
Sinus  alae  parvae,  3 

cavemosus,  3 

circularis,  4 

durae  matris,  2 

intercavemosus  anterior,  3 
posterior,  3 

occipitalis,  2 

petrosus  inferior,  3 
superior,  3 

rectus,  2 

sagittalis  inferior,  2 
superior,  2 

transversi,  2 
Sixth  nerve,  3 

ventricle,  335,  337 
Slender  lobules,  255,  255 
Smelling  brain,  77 
Solitary  cells  of  Meynert,  195 

tract,  295,  297,  302,  305,  423 
SomfEsthetic  area,  64,  98,  181 
Special  nuclei  of  medulla,  302,  310 

sensations,  383 

sense  fibers  of  internal  capsule, 

104,  115,  226 
nuclei,  322 

Speech  center,  60,  i75>  178,  182 
Spheno-parietal  sinus,  3,  4 
Spinal  bulb,  284 

cord.  31,  SS3'  334,  335,  34i, 

426 
ganglion.  334,  364,  401,  428 

neurones,  165,  400,  401 
reflexes,  390 

tract  of   trigeminal  nei-ve,   278, 
301,  423,  424 
Spino-cerebral  reflexes,  393 
Spino-thalamic  tract,  161,  231,  275, 
274,    287,    295,    297,    299', 

305,  311,  341,  345,  356 

Spino-vestibular  tract,  357 
Splenium  of  corpus  callosum,  75,  95, 

105,  108,    113,   109,    121, 

131 

Spongioblasts,  398,  399 
Stalk  of  pineal  body,  87,  149 
Stellate  cells  of  cerebellum,  257,  259 
Stem  of  fissura  cerebri  lateralis,  57 
Stereognosis.  377 


Stereognostic  center,  64,  98,  182, 183 

Stilling's  nuclei,  262 

Stilling  and  Clark  (nucleus  of),  348 

Straight  gyrus,  74,  75 

sinus,  2,  3,  4 
Strand  cells,  340 
Stratum  cinereum,  256 
gangliosum,  256,  257 
granulosum,  256,  258 
griseum  centrale.  152, 157, 159 
221,  222 
of  superior  coUiculus,  163,  219 
intermedium,  208,  225 
interolivare  lemnisci,  292 
nucleare,  278,  293,  302,  303 
zonale  of  cerebral  cortex,  184 
of  corpora  quadrigeniina,  163, 

219 
of  thalamus,  140,  208 
Stria  intermedia,  77,  78,  267 
lateralis,  78,  267 
medialis,  77,  78,  267 
medullaris  thalami,  87,  91,  95, 

T-35^  137,  212,  239,  239 
terminalis,  loi,    109,   115,   119, 
124,  125,  207,  239,  412 
Stride  medullares,  149,  270,  290,  309 

olfactoriae,  78,  267 
Striato-tbalamic  fibers,  207 
Structure  of  arachnoid,  8, 
of  cerebrum,  164 
and  relations  of  dura  mater,  i 
and  relations  of  pia  mater,  9 
Subarachnoid  rivulets,  8 
septum,  327,  329 
space,  6,  8,  9,  329 
Subcallosal  gyrus,  97,  107,  414 
Subdural  space,  329 
Subiculum,  199,  201 
Subparietal  point,  55 

sulcus,  86,  91,  95 
Substantia  alba  spinahs,  351 
corticalis  cerebelli,  242,  256 

cerebri,  177 
gelatinosa  centralis,  173,  339 

(Roland^.),  339,  345,  347 
nigra,  30,    loi,    145,  146,  151, 

157,  159,  161,  221 
perforata  anterior,  38,  75,  79,  200 

posterior,  38,  75,  151 
reticularis,    291,  295,  297,  302, 

303'  305,  423 
spongiosa,  339 


INDEX. 


451 


Sulci,  52 

occipitalcs  laierales,  61,  68 

of    cerebellum,    247,    248,    252, 

420 
of  convex  surface  of  cerebrum,  52 
of  lower  surface  of  cerebellum, 

252,  253 
of  lower  surface  of  cerebrum,  73 
of  medial  surface  of  cerebrum, 

85 
of  upper  surface  of  cerebellum, 
248,  249 
Sulcus  basilaris,  153,  272 

centralis  (Rolandi),   39,  53,  56, 
57,  61,  410 
insulse,  65,  72 
cinguli,  25,  86,  91,  95,  410 
circularis  insuhe,  70,  71,  75,  125 
corporis  callosi,  86,  91 
ectorhinalis,  80,  86,  90 
frontalis  inferior,  59,  61 
medius,  59,  60,  61 
superior,  59,  61 
horizontalis  cerebelli,  247 
hypothalamicus,    91,    139,   405, 

415,. 

intermedius  posterior,  335,  338 

interparietalis,  61,  63 

lateralis  anterior,  41,  286,  338 
mesencephali,  146,  159,   161 
posterior,  41,  286,  337 

limitans,  269,  270,  290,  418 

nervi  oculomotorii,  146 

occipitalis  transversus,  61,  68 

occipito-parietalis,  58,  61,  86 

orbitalis,  74,  75 

paramedians,  59,  61 

parolfactorius  anterior,  47,  75, 

79 

posterior,  75,  77,  79,  95 
prascenlralis  cerebelli,  248 

inferior,  59,  61 

superior,  59,  61 
pi'aedeclivis  cerebelli,  249 
praepyramidalis  cerebelli,  252 
postcentralis  cerebelli,  248 

inferior,  61,  63 

superior,  61,  63 
postdeclivis  cerebelli,  249 
postnodularis  cerebelli,  252 
postpyramidalis  cerebelli,  253 
rhinalis,  80 
subparietalis,  86,  91 


Sulcus  temporalis  inferior,  70,  80,  86 
medius,  61,  63,  70 
superior,  61,  63,  70 
vallecukc,  251,  252 
Superciliary  border,  39,  52 
Superficial  annectant  fO'r'^s,  64 
layer  of  cerebellar  cortex,  256 
middle  cerebral  vein,  23 
transverse    fibers    of   pons,   271, 
275 
Superior  cerebellar  artery,   15,  27 

peduncle   (sec  brachium   con- 
junctivum) 
cerebral  veins,  22 
colliculus     of    corpora     cjuadri- 

gemina,  157,  219 
commissure  (Meynerti),  208,  218, 

221 
efferent  veins  of  pons,  27 
external  cerebellar  veins,  29 
fillet,  159,  160,  274,  296 
fovea,  270 

frontal    gyrus,    39,   59,   60,  61, 
209 
sulcus,  39,  57,  59,  414 
glossopharyngeal  ganglion,  46 
lamina  of  internal  capsule,   100, 

113,  115,  226 
longitudinal  fasciculus,  240 
medullary  velum,    13,  87,  146, 
147,  149,  245,  246,  247, 
252,  262,  263,  275 
nucleus  of  Bechterew  and  Flech- 

sig,  308 
uccipital  g}rus,  43,  61,  68,  69 
olivary  nucleus,   277,   278,    279 

280 
parietal  lobule,  43,  61,  63,  64 
peduncle  of  cerebellum,  245 
petrosal  sinus,  3,  4,  5 
postcentral  sulcus,  57,  63 
preccntral    sulcus,    39,    57,  59, 

410,  414 
quadrigeminal    colliculus,     137, 

204,  219,  418 
sagittal  sinus,  2,  3,  5,  6 
semilunar  lobule,  243,251,255, 

420 
surface  of  cerebellum,  243,  248 

of  temporal  lobe,  70 
temporal  g}Tus,  61,  70,  71 
sulcus.  57,  63,  70.  410 
Supero-medial  border,  39,  52 


452 


INDEX. 


Supracallosal  g>'rus,  97,  107,  414 
Supramarginal  gyrus.  43,  61,  63,  67 
Supraradiary  zone  of  cerebral  cortex, 

184 
Surface  of  cerebellum,  248 

of  cerebrum,  34,  51 
Surfaces  of  m-edulla  oblongata,  286 

of  mid-brain,  144 

of  pons,  266 

of  spinal  cord,  337 

of  thalamus,  140 
Sustentacular  tissue,  167,  173 
Sylvian  point,  55 

Taenia  semicircularis,   115,  119,  125 
(see  stria  terminalis) 

terminalis,  119 

ventriculi  quarti,  149,  270,  297 
Tapetum,  123,  124,  131,  137,  239 
Tassel  neurones,  199 
Tegmental  decussations,  156 

hypothalamic  region,  143 
Tegmentum,  a,  of  mid-brain,  30,  75, 

109,  132,  146,  152 
Tela  chorioidea  ventriculi  quarti,  10 

tertii,  10 
Telencephalon,   28,  30,  402,  403,  404 
Telodendria,  167,  169 
Temporal  arteiT,  17 

lobe  of  cerebrum,  37,  53,  69,  75, 
91,  98 

pole,  53,  70 
Temporo-occipital  gyrus,  81,  97 

sulcus,  81 
Temporo-parietal  artery,  19 
Temporo-pontal  tract,  100,  148,  159, 

225,  226 
Temporo-thalamic     radiation,      100, 

226,  233,  310 
Tentorial  area  of  cerebellum,  248 

of  cerebrum,  79 
notch,  2,  4 
Tentorium  cerebelli,  2,  3,  4 
Terminal  ganglia,  401 

nuclei  of  optic  nerve,  315,  323 
nucleus,  42,  319,  322,  349,  364, 365 
of  olfactory  nerves,  42,  196 
Tertiary  sulci,  411 

Thalamus,  i.,  28, 30, 37, 51,101, 105, 

119,   125,   139^   145,    147, 

157,  208,  209,  416,  417 

Thalamo-mammillary   fasciculus    (of 

Vicq  d'Azyr),  145,  222,  237 


Thalamo -striate  fibers,  208 
Third  cerebral  vesicle,  35 
nerve,  3,  4,  5,  42 
ventricle,  9,  30,  34,  37,  loi,  iii, 
127,  137,  145,  209 
Threshold  of  island,  72.  77 
Tigroid  bodies,  167 
Tonsil  of  cerebellum,  245,  252,  254, 

420 
Torcular  herophili,  2 
Tracing  of  impulses,  366 
Tracts  of  fibers  in  tegmentum,  156 
of  spinal  cord,  341,  345,  354, 
429 
Trac.tus  cerebro-cortico-pontalis  fron- 
tahs,  103,  151,  225 
temporalis,  100,  148,  225 
cerebro-spinalis  pyramidalis,  226 
intermedius,  100,  148,  225 
olfactorius,  77,  78 
optici,  8^ 
solitarius,  285,  295,  297,  302, 

422,  423 
spinalis  n.  trigemini,  277,  278, 
288,   295,   297,  301,   305, 

311 

Transverse  fibers  of  medulla,  291 
of  pons,  271 
of  spinal  cord,  351 
fissure  of  cerebellum,  36 

of  cerebrum,  35,  43,  53,  55, 
109,  411 
occipital  sulcus,  43,  57,  68,  69 
sinuses,  2,  3,  4,  5 
temporal    gyri,    70,    105,    121, 
125 
sulci,  70 
Trapezoid  body,  271,  272,  277,  280 
Triangle  of  habenula,  140 

of  lateral  fillet,  152,  164 
Triangular  tract  of  Helwig,  298,  305, 

311,312,  341,  345,  357 
Trigeminal  nerve,  41,  45,  153,  209, 
320,  321 
nucleus,  224 
Trigonum   vagi,    290,  317,    (see    ala 
cinerea) 
•  coUaterale,  123,  124 
habenulaj,  140,  137,   243 
n.  hypoglossi,  149,  270 
olfactorium,  47,  75,  77,  79,  200 
Trochlear  nerve,  45,  146,  147,  321 
nucleus,  223 


INDEX. 


453 


Trolard's  great  anastomotic  vein,  23 
Truncus   of    corpus    callosuni,    95, 

108 
Tuber  annulare,  266 

cinereum,    30,    38,  47,  75,  82, 
84,  87,  221,  267,  415 

vermis,  87,  247,  252,  255 
Tuberculum  anterior  thalami,  140 

acusticum,  149,  309 

cinereum,  13,  289,  301 
Twelfth  nerve,  3,  49,  322 
Types  of  neurones.  168 

Uncinate  fasciculus,  237,  239,  240 
Uncrossed  ponto-spinal  tract,  280,  373 
Uncus  hippocampi,  82,  94,  196,  235 
Unipolar  neurones,  400,  401 
Uvula  vermis  cerebelli,  87,  245,  247, 
252,  254 

Vagus  nerve,  5,  46,  153,  209,  293, 

321 
Vallecula  cerebelli,  36,  244,  251 
Valve  of  Vieussens,  246 
Veins  of  cerebellum,  29 
of  cerebrum,  21 
of  medulla,  24 
of  pia  mater,  13 
of  spinal  cord,  331,  332 
Velum  interpositium,  135  (see  chorioid 
tela  of  third  ventricle) 
medullare  inferius,  244 
superius,  245,  263 
Vena  basilaris,  23 

cerebri  interna,  21 
magna,  21 
media,  23 
terminalis,  235 
Venae  cerebelli  inferiores,  29 
superiores,  29 
cerebri,  21 
extemse,  22 
inferiores,  23 
mediales,  22 
superiores,  22 
spinales  extreace,  332 
internae,  332 
Ventral  cochlear  nucleus,  309 

longitudinal  fibers  of  pons,  272 
stalk  of  thalamus,  100,  212,  226, 
2?  2 


Ventral  tegmental  decussation,    156, 

157,  159 
zone,  399,  422,  427 
Ventro-latcral    cells   of    cord,    341, 

345,  343 
Ventro-medial  cells  of  cord,  34i,345> 

340 
Ventricle  of  corpus  callosum,  89 
Ventricular  gray  matter  of  cerebrum, 

221 
Ventriculus  lateralis,  112 
quartus,  313 
terminalis,  337,  426 
tertius,  127 
Vermis  cerebelli,  242,  243,  419 
inferior,  244 
superior,  244 
Vertebral  artery,  3,  5,  14,  15,  27 

ganglia,  401 
Vessels  of  arachnoid,  9 
Vestibular  nerve,  280,  293,  320,  386 
mucleus,   295,   297,  283,  302, 

307 
path,  386 
Vestibulo-spinal  reflex,  393 
Vicq  d'Azyr  (foramen  of),  153 
Vicq    d'Azyr's    fasciculus    thalamo- 
mammillaris,  85,   no,  222, 
237 
Vieussens's  medullary  velum,  146 

valve,  246 
Vinculum,  a,  cerebelli,  250 
Vision,  center  for  macular,  67 
Visual  center  (receptive),  81,  98,  192 
memory  center,  67,  69 

Wallerian  degeneration,  171 
White  anterior  commissure,  335,  351 
matter  of  cerebellum,  262 

of  cerebrum,  224 

of  medulla,  290 

of  pons,  270 

of  spinal  cord,  351 

of  thalamus,  208 
Worm  of  cerebellum,  243 
Writing  center  of  Gordinier,  175, 178, 
182 

Zonal  layer  of  cerebral  cortex,  1S4 
Zones  of  embryo,  ventral  and  dorsal, 
399 


QJ.I451 

Semtee 

Anatomy  of  the  brain  and 
spinal  cord  === 


Sa5 
1907 


OCT    12   1909 


